fix(plugins): web mode lookups use the modes the display registered (#668)

A plugin may compute its display modes from its config: soccer-scoreboard
registers soccer_<league>_live/recent/upcoming for every custom_leagues
entry, which no manifest can list ahead of time. The display always rotated
them (_register_loaded_plugin prefers plugin.modes), but the web process
reads plugins as files, so /display/modes, the on-demand dialog and
on-demand/start with a mode and no plugin_id saw only manifests -- a custom
league's mode was missing from every list and 404'd on lookup.

- PluginStateManager.record_modes(): the controller records what it
  registered, on the loaded record (an unload or reload forgets it)
- the runtime snapshot carries it per plugin as "modes" (bounded), and
  PluginRuntimeView.display_modes() reports it only while live
- PluginCatalog takes a runtime_source; get_plugin_display_modes and
  find_plugin_for_mode prefer the live modes, falling back to the manifest
  when the display is stopped or has not loaded the plugin. The view is read
  at most once a second, so a listing is one read, not one per plugin.

No manifest or plugin change needed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/test_plugin_runtime_snapshot.py

@@ -162,7 +162,7 @@ class TestPublisher:
         assert snapshot["stale_after"] == rt.STALE_AFTER
         assert snapshot["plugins"] == {"clock": {
             "loaded": True, "state": "enabled", "error": None,
-            "version": "1.0.0", "loaded_at": 10.0}}
+            "version": "1.0.0", "loaded_at": 10.0, "modes": None}}
 
     def test_changes_are_throttled_and_quiet_displays_refresh(self):
         cache = MagicMock()