feat(plugins): add theme contributions

Adds plugin-contributed light and dark app themes, including persistence, host-aware coalescing, fallback behavior, documentation, examples, and browser/iOS QA.

packages/server/src/server/plugins/compiler.ts

@@ -81,6 +81,7 @@ const REGISTRATIONS_REMOVED_BY_TARGET: Record<PluginBuildTarget, ReadonlySet<str
     "addWorkspacePanel",
     "addCommandCenterItem",
     "addAttachmentSource",
+    "addTheme",
   ]),
 };
 

packages/server/src/server/websocket-server.ts

@@ -1676,6 +1676,8 @@ export class VoiceAssistantWebSocketServer {
         plugins: true,
         pluginManagement: true,
         pluginLogs: true,
+        // COMPAT(pluginThemes): added in v0.5.0, remove gate after 2027-08-20.
+        pluginThemes: true,
         // COMPAT(skillManagement): added in v0.4.0, remove gate after 2027-08-16.
         skillManagement: true,
         // COMPAT(terminalRestoreModes): added in v0.1.81, remove gate after 2026-11-23.