feat(element-style): visibility, alignment and scale per element

Completes the customization vocabulary: hide an element, align it, and
resize a logo, alongside the font/size/colour/offset that already existed.
All three per mode.

They resolve to "change nothing" until the user asks for something -- True,
None and 1.0 -- rather than to whatever the schema declares. That is the
same invariant the font fields keep: a caller that honours them still
renders an untouched config exactly as it did before they existed. A
schema default therefore does not count as a choice, which matters because
the save flow writes that default into config either way.

scale sits in the layout block with the offsets rather than in the element
block, because it is geometry: a logo has a scale and no font. The widget's
columns come from the schema, so a logo row shows visibility, offsets and
scale and no empty font cell.

Two bugs found by the tests rather than by reading:

- A nullable enum needs null in its enum list, not just in its type. The
  mode copy of `align` defaulted to null and then failed its own schema, so
  a plugin declaring any enum field with modes could not save at all. Six
  tests failed on this before any of them reached what they were testing.
- defaults_from_schema only ever extracted font/font_size/text_color, so
  the schema defaults for the new fields were invisible to the resolver and
  a declared default read as a user choice.

Widget: the table scrolls horizontally and pins the element-name column.
Nine columns do not fit the config panel, and clipping them hid the offsets
entirely while scrolling them made every row anonymous.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

test/test_element_style.py

@@ -824,3 +824,160 @@ class TestModeSaveRoundTrip:
                 "font_size": 99}}}}}, defaults)
         ok, _errors = sm.validate_config_against_schema(merged, schema)
         assert not ok
+
+EXTRA_SCHEMA = {
+    "type": "object",
+    "properties": {
+        "customization": {
+            "type": "object",
+            "x-style-modes": ["live"],
+            "x-style-elements": {
+                "score_text": {
+                    "title": "Score",
+                    "font": {"default": "PressStart2P-Regular.ttf"},
+                    "size": {"default": 10},
+                    "color": {"default": [255, 255, 255]},
+                    "visible": True,
+                    "align": {"default": "center"},
+                    "offsets": True,
+                },
+                "home_logo": {
+                    "title": "Home Logo",
+                    "offsets": True,
+                    "visible": True,
+                    "scale": {"default": 1.0, "min": 0.25, "max": 4},
+                },
+            },
+        },
+    },
+}
+
+
+@pytest.fixture
+def extra_schema_path(tmp_path):
+    path = tmp_path / "extra_schema.json"
+    path.write_text(json.dumps(EXTRA_SCHEMA), encoding="utf-8")
+    return str(path)
+
+
+class TestVisibleAlignScale:
+    """visible / align / scale all resolve to "change nothing" until asked.
+
+    That is the same invariant the font fields keep: a caller that honours
+    these must still render an untouched config exactly as it did before
+    they existed, so the neutral values are True / None / 1.0 rather than
+    whatever the schema happens to declare.
+    """
+
+    def _style(self, config, mode=None, schema=None):
+        defaults = defaults_from_schema_file(schema) if schema else {}
+        return ElementStyleResolver(config, defaults, mode=mode).style(
+            "score_text", classic_font="PressStart2P-Regular.ttf",
+            classic_size=10, classic_color=(255, 255, 255))
+
+    def test_an_untouched_config_is_neutral(self, extra_schema_path):
+        st = self._style({}, schema=extra_schema_path)
+        assert (st.visible, st.align, st.scale) == (True, None, 1.0)
+
+    def test_a_schema_default_is_not_a_choice(self, extra_schema_path):
+        """align defaults to 'center' in the schema, and the save flow writes
+        that into config -- which must not read as the user asking for it."""
+        config = {"customization": {"score_text": {"align": "center",
+                                                   "visible": True}}}
+        st = self._style(config, schema=extra_schema_path)
+        assert st.align is None, "the plugin keeps its own alignment"
+        assert st.visible is True
+
+    def test_hiding_an_element(self, extra_schema_path):
+        config = {"customization": {"score_text": {"visible": False}}}
+        assert self._style(config, schema=extra_schema_path).visible is False
+
+    def test_a_real_alignment_choice_comes_through(self, extra_schema_path):
+        config = {"customization": {"score_text": {"align": "right"}}}
+        assert self._style(config, schema=extra_schema_path).align == "right"
+
+    @pytest.mark.parametrize("written,expected", [
+        ("left", "left"), ("RIGHT", "right"), ("  center ", "center"),
+        ("centre", "center"), ("middle", "center"),
+        ("sideways", None), ("", None), (5, None), (None, None),
+    ])
+    def test_alignment_coercion(self, written, expected, extra_schema_path):
+        config = {"customization": {"score_text": {"align": written}}}
+        assert self._style(config, schema=extra_schema_path).align == expected
+
+    @pytest.mark.parametrize("written,expected", [
+        (2, 2.0), (0.5, 0.5), ("1.5", 1.5),
+        (0, 1.0), (-3, 1.0),          # nonsense degrades, never inverts
+        (999, 10.0),                  # clamped: the panel is 32px tall
+        ("huge", 1.0), (None, 1.0), (True, 1.0),
+    ])
+    def test_scale_coercion(self, written, expected, extra_schema_path):
+        config = {"customization": {"layout": {"score_text": {"scale": written}}}}
+        assert self._style(config, schema=extra_schema_path).scale == expected
+
+    def test_scale_reads_from_the_layout_block(self, extra_schema_path):
+        """scale is geometry, so it sits with the offsets -- a logo has a
+        scale and no font."""
+        config = {"customization": {"layout": {"score_text": {"scale": 2}}}}
+        assert self._style(config, schema=extra_schema_path).scale == 2.0
+
+    @pytest.mark.parametrize("field,value,attr,expected", [
+        ("visible", False, "visible", False),
+        ("align", "right", "align", "right"),
+    ])
+    def test_a_mode_overrides_them(self, field, value, attr, expected,
+                                   extra_schema_path):
+        config = {"customization": {"modes": {
+            "live": {"score_text": {field: value}}}}}
+        st = self._style(config, mode="live", schema=extra_schema_path)
+        assert getattr(st, attr) == expected
+
+    def test_a_mode_overrides_scale(self, extra_schema_path):
+        config = {"customization": {
+            "layout": {"score_text": {"scale": 2}},
+            "modes": {"live": {"layout": {"score_text": {"scale": 3}}}}}}
+        assert self._style(config, mode="live",
+                           schema=extra_schema_path).scale == 3.0
+
+    def test_an_unset_mode_field_inherits_the_base(self, extra_schema_path):
+        config = {"customization": {
+            "score_text": {"visible": False},
+            "modes": {"live": {"score_text": {"align": "right"}}}}}
+        st = self._style(config, mode="live", schema=extra_schema_path)
+        assert st.visible is False and st.align == "right"
+
+
+class TestExtraFieldSchema:
+    def _props(self):
+        return expand_style_elements(
+            EXTRA_SCHEMA)["properties"]["customization"]["properties"]
+
+    def test_only_declared_subfields_are_emitted(self):
+        """home_logo declares no font, so it gets no font control."""
+        assert list(self._props()["home_logo"]["properties"]) == ["visible"]
+
+    def test_a_text_element_gets_the_text_fields(self):
+        assert list(self._props()["score_text"]["properties"]) == [
+            "font", "font_size", "text_color", "visible", "align"]
+
+    def test_scale_is_emitted_with_the_offsets(self):
+        layout = self._props()["layout"]["properties"]
+        assert list(layout["home_logo"]["properties"]) == [
+            "x_offset", "y_offset", "scale"]
+        assert list(layout["score_text"]["properties"]) == [
+            "x_offset", "y_offset"], "scale is opt-in"
+
+    def test_declared_scale_bounds_are_kept(self):
+        scale = self._props()["layout"]["properties"]["home_logo"]["properties"]["scale"]
+        assert (scale["minimum"], scale["maximum"]) == (0.25, 4)
+
+    def test_align_offers_only_valid_choices(self):
+        align = self._props()["score_text"]["properties"]["align"]
+        assert align["enum"] == ["left", "center", "right"]
+
+    def test_the_mode_copies_are_nullable(self):
+        live = self._props()["modes"]["properties"]["live"]["properties"]
+        assert live["score_text"]["properties"]["visible"]["default"] is None
+        assert "null" in live["score_text"]["properties"]["visible"]["type"]
+        scale = live["layout"]["properties"]["home_logo"]["properties"]["scale"]
+        assert scale["default"] is None and "null" in scale["type"]