docs(plugins): how to declare styleable elements; harden the widget's lookups

The plugin-author guide for the compact x-style-elements declaration -- what
each key does, how to read values back without breaking the "user-forced only
when it differs from the default" rule, and why a hand-written block needs no
changes to be adopted.

Also clears the static-analysis findings on style-editor.js. Every lookup in
that file is keyed by something out of a schema or a saved config, so a key of
__proto__ or constructor would walk the prototype chain and hand back a
function instead of a schema; reads now go through an own-property helper. The
panel registry became a list, and the flagged vars moved to their function
roots.

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

docs/PLUGIN_ELEMENT_STYLING.md

@@ -0,0 +1,135 @@
+# Per-element styling for plugin authors
+
+Users want to change the font, size and colour of individual things on screen,
+nudge them a few pixels, hide the ones they do not care about, and scale a logo
+down. This is the one system that does that, and a plugin joins it by
+**declaring elements in its `config_schema.json`** — not by writing a style
+resolver, a font cache or a web form.
+
+The short version:
+
+```jsonc
+"customization": {
+  "type": "object",
+  "title": "Display Customization",
+  "x-style-elements": {
+    "score_text": {
+      "title": "Score",
+      "font":  { "default": "PressStart2P-Regular.ttf" },
+      "size":  { "default": 10, "min": 4, "max": 16 },
+      "color": { "default": [255, 255, 255] },
+      "offsets": true,
+      "visible": true,
+      "align": true
+    },
+    "home_logo": { "title": "Home logo", "offsets": true, "scale": true }
+  },
+  "x-style-modes": ["live", "upcoming", "recent"]
+}
+```
+
+That is the whole declaration. The core expands it into a full JSON Schema, the
+web UI renders a compact style editor with a row per element, and the values
+land in `config.json` under the keys you named.
+
+## What each key does
+
+| Key | Effect |
+|---|---|
+| `font` | Font picker listing every shipped **and user-uploaded** font. |
+| `size` | Number field. `min`/`max` also cap which fixed-size fonts are offered. |
+| `color` | Colour swatch; stored as `[r, g, b]`. |
+| `offsets` | X/Y nudge, stored under `customization.layout.<element>`. |
+| `visible` | Show/hide toggle. |
+| `align` | `left` / `center` / `right`. |
+| `scale` | Size multiplier, for logos and images. Also under `layout`. |
+
+`x-style-modes` is optional. Declare it and every element gains a per-mode
+override tab — a scoreboard can then style its live, upcoming and recent cards
+separately. **A mode field left blank means "inherit", not zero.**
+
+## Reading the values
+
+Every plugin inherits `BasePlugin.styles`, which finds your `config_schema.json`
+on its own:
+
+```python
+style = self.styles.style(
+    "score_text",
+    classic_font="PressStart2P-Regular.ttf",   # what you shipped
+    classic_size=10,
+    classic_color=(255, 255, 255),
+)
+if style.visible:
+    draw.text((x + style.offset[0], y + style.offset[1]),
+              text, font=style.font, fill=style.color)
+```
+
+For a specific mode, use `self.styles_for("recent")`, or set
+`STYLE_MODE = "recent"` on the class and keep calling `self.styles`.
+
+### The one rule that matters
+
+**Pass your shipped values as the `classic_*` arguments.** The resolver returns
+them verbatim unless the user actually changed something, which is what keeps an
+untouched install rendering byte-identically. It can tell the difference because
+a value only counts as user-forced when it *differs from the schema default* —
+the save path writes the full default object into `config.json` on every save,
+so "present in config" proves nothing.
+
+Never compare against the default yourself; that rule lives in exactly one place.
+
+### Stateless readers
+
+For helpers handed a config dict rather than a plugin instance:
+
+```python
+from src.element_style import (element_color, element_visible,
+                               element_align, element_scale, layout_offset)
+
+colour = element_color(config, "score_text", (255, 255, 255), mode)
+shown  = element_visible(config, "records", True, mode)
+dy     = layout_offset(config, "score", "y_offset", 0, mode)
+```
+
+## Sports scoreboards
+
+`SportsCoreSharedMixin` wires most of this up already. Two things to know:
+
+* **Name your draws.** `_draw_text_with_outline(..., element="score_text")`
+  resolves the colour by name *and* honours the visibility toggle. Without it
+  the colour has to be guessed from the identity of the font object, which
+  cannot tell two elements apart when they share a face — the case every
+  bitmap font is in.
+* **Modes are free.** Live/upcoming/recent are separate instances, so setting
+  `SKIN_MODE` on each is enough; no call site passes a mode.
+
+## Adopting an existing hand-written block
+
+If your schema already spells out `font` / `font_size` / `text_color` per
+element longhand, **you do not need to change anything**. The core recognises
+that shape and upgrades it in place: the style editor, the real font picker
+(including uploaded fonts) and per-mode overrides all appear on a core update.
+Add `x-style-modes` if you want the mode tabs.
+
+## Fonts, and why size is sometimes locked
+
+32 of the 35 shipped fonts are fixed-strike BDF bitmaps: they render at exactly
+one pixel size and ignore `font_size`. The picker knows which, and the editor
+locks the size field to the native size and labels it `fixed`. A font too tall
+for the `max` you declared is not offered at all.
+
+Uploaded fonts (Fonts tab) land in `assets/fonts/` and appear in the picker
+automatically.
+
+## Checklist
+
+1. Declare `x-style-elements` (and `x-style-modes` if you have modes).
+2. Read through `self.styles`, passing your shipped values as `classic_*`.
+3. Honour `style.visible`, `style.offset` and `style.scale` where they apply.
+4. Confirm an untouched config renders identically:
+   `python scripts/check_plugin.py --plugin <id>`.
+5. Monorepo plugins: bump `manifest.json` and run `python update_registry.py`.
+
+See also: [docs/PLUGIN_CONFIGURATION_GUIDE.md](PLUGIN_CONFIGURATION_GUIDE.md),
+[docs/FONT_MANAGER.md](FONT_MANAGER.md).