feat: implemented plugin configuration UI and calendar event action slot

- Add configSchema support to plugin manifest and ServerPlugin registry
- Add schema-driven admin config page (string, secret, boolean, number, select fields)
- Add per-plugin config storage backend (JSON files + REST API)
- Add calendar-event-actions and admin-plugin-page slot names to plugin store
- Add registerCalendarEventAction and registerAdminPage to plugin API
- Add calendarFormHooks (onCalendarEventFormOpen/Save) to hook bus
- Add PluginSlot in calendar event modal for plugin action buttons
- Style calendar event action buttons to match Bulwark outline button design
- Add Configure link per plugin in admin plugins dashboard
- Add Jitsi Meet plugin with tests (repos/plugins/jitsi-meet)
- Exclude data/admin/plugins from ESLint (deployed plugin bundles)

app/api/admin/plugins/route.ts

@@ -157,6 +157,9 @@ export async function POST(request: NextRequest) {
       permissions: (manifest.permissions as string[]) || [],
       entrypoint: manifest.entrypoint as string,
       enabled: true,
+      ...(manifest.configSchema && typeof manifest.configSchema === 'object'
+        ? { configSchema: manifest.configSchema as ServerPlugin['configSchema'] }
+        : {}),
       installedAt: now,
       updatedAt: now,
     };