feat: ship src/element_style — the per-element style resolver plugins already expect

Three plugins (of-the-day, ledmatrix-music, football-scoreboard) import
src.element_style behind guarded try/except with classic fallbacks, but
the module never existed in core, so the richer per-element styling UI
those code paths implement has been dormant. This lands it:

- ElementStyleResolver.style() resolves per-element font/size/color with
  the key semantic the consumers encode: a config value counts as
  user-forced only when it differs from the schema default (the web UI
  bakes defaults into config.json on save), and untouched configs
  resolve to exactly the caller's classic values — byte-identical
  rendering, proven by of-the-day's committed goldens passing unchanged.
- defaults_from_schema_file parses both declaration forms (the compact
  x-style-elements map and hand-written customization blocks).
- expand_style_elements() expands x-style-elements into full config
  blocks; schema_manager.load_schema() applies it (guarded, no-op for
  schemas without the declaration) so the config form and defaults
  merging see the expanded UI.
- Fonts resolve cwd-independently with (path, size) caching; .bdf loads
  via freetype like FontManager; nothing in the module raises out of
  style().

Verified: 31 new unit tests; of-the-day's previously-skipped 9-test
spec suite now runs and passes; football's resolver tests pass (27);
music's 38 plugin tests pass; schema-manager suites pass (43).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FgbA8SMutQQpXkMG8LMmC4

src/plugin_system/schema_manager.py

@@ -115,7 +115,17 @@ class SchemaManager:
             if not isinstance(schema, dict):
                 self.logger.error(f"Invalid schema format for {plugin_id}: not a dictionary")
                 return None
-            
+
+            # Expand any customization.x-style-elements declaration into the
+            # full per-element style blocks (font/size/color + layout
+            # offsets) the web-UI config form renders. No-op for schemas
+            # without the declaration; never raises.
+            try:
+                from src.element_style import expand_style_elements
+                schema = expand_style_elements(schema)
+            except ImportError:
+                pass
+
             # Cache the schema
             self._schema_cache[plugin_id] = schema