feat(mcp): introduce OAuth 2.1 auth and enforce addon gating

OAuth 2.1 authentication for MCP:
- Add OAuth 2.1 authorization server with PKCE support (routes/oauth.ts)
- Add OAuth service for client CRUD, auth-code flow, and token management (services/oauthService.ts)
- Add typed scope definitions and enforcement helpers (mcp/scopes.ts)
- Add OAuth consent UI page (OAuthAuthorizePage.tsx)
- Add client-side scope labels and descriptions (api/oauthScopes.ts)
- Integrate OAuth token auth into MCP handler alongside existing static tokens
- All OAuth endpoints gated on `mcp` addon

Addon gating across MCP tools, resources, and prompts:
- Add typed ADDON_IDS constant (server/src/addons.ts) replacing all string literals
- Gate budget tools and resources (trip-budget, per-person, settlement) on `budget` addon
- Gate packing tools and resources (trip-packing, trip-packing-bags, trip-todos) on `packing` addon
- Gate todos tools on `packing` addon (mirrors web UI Lists tab behavior)
- Expand atlas gate to cover full tool body (bucket-list + country tools no longer leak)
- Expand collab gate to cover full tool body (collab notes no longer leak)
- Gate packing-list and budget-overview MCP prompts on their respective addons
- Gate get_trip_summary sections per addon; blank packing/budget/collab_notes/todos when disabled
- Remove trip-files resource and files field from get_trip_summary
- Replace all isAddonEnabled('literal') calls with ADDON_IDS constants

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/mcp/tools/notifications.ts

@@ -11,11 +11,15 @@ import {
   TOOL_ANNOTATIONS_DELETE, TOOL_ANNOTATIONS_NON_IDEMPOTENT,
   demoDenied, ok,
 } from './_shared';
+import { canRead, canWrite } from '../scopes';
+
+export function registerNotificationTools(server: McpServer, userId: number, scopes: string[] | null): void {
+  const R = canRead(scopes, 'notifications');
+  const W = canWrite(scopes, 'notifications');
 
-export function registerNotificationTools(server: McpServer, userId: number): void {
   // --- NOTIFICATIONS ---
 
-  server.registerTool(
+  if (R) server.registerTool(
     'list_notifications',
     {
       description: 'List in-app notifications for the current user.',
@@ -32,7 +36,7 @@ export function registerNotificationTools(server: McpServer, userId: number): vo
     }
   );
 
-  server.registerTool(
+  if (R) server.registerTool(
     'get_unread_notification_count',
     {
       description: 'Get the number of unread in-app notifications.',
@@ -45,7 +49,7 @@ export function registerNotificationTools(server: McpServer, userId: number): vo
     }
   );
 
-  server.registerTool(
+  if (W) server.registerTool(
     'mark_notification_read',
     {
       description: 'Mark a single notification as read.',
@@ -62,7 +66,7 @@ export function registerNotificationTools(server: McpServer, userId: number): vo
     }
   );
 
-  server.registerTool(
+  if (W) server.registerTool(
     'mark_notification_unread',
     {
       description: 'Mark a single notification as unread.',
@@ -79,7 +83,7 @@ export function registerNotificationTools(server: McpServer, userId: number): vo
     }
   );
 
-  server.registerTool(
+  if (W) server.registerTool(
     'mark_all_notifications_read',
     {
       description: "Mark all of the current user's notifications as read.",