fix(web): a store install asks for a restart by the id it installed as

POST /plugins/install decides restart_required from whether config.json
already enables the plugin: the display loads a plugin when its enabled
flag changes, so one already enabled (a reinstall, or a config carried
over) keeps running the copy it loaded until a restart. The route read
that flag under the registry id. Weather, Music, Stocks and Leaderboard
install under the id their manifests declare (weather ->
ledmatrix-weather), which is the config section's id, so reinstalling an
enabled one never reported that a restart was needed.

Both the queued and the direct path now look up the installed id once
(#746's _installed_plugin_id) and use it for the plugin_id they answer
with and for the enabled check.

Tests: test/test_api_v3_install_restart_installed_id.py, through the
Flask test client, both paths.

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

CHANGELOG.md

@@ -897,6 +897,13 @@ policies are unchanged.
   string counts, anything else that is not a finite number (or a
   `get_display_duration()` that raises) pauses for 30 s, and a number at or
   below zero for 15 s, with one warning per plugin.
+- Reinstalling Weather, Music, Stocks or Leaderboard from the Plugin Store
+  while it is enabled asks for a display restart, as reinstalling any other
+  enabled plugin does. `POST /api/v3/plugins/install` looked for the
+  plugin's `enabled` flag under the store id (`weather`), but its config
+  section is under the id its manifest declares (`ledmatrix-weather`), so
+  `restart_required` was always false and the display kept running the
+  copy it had loaded. The check now uses the installed id.
 
 ### Scrolling