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/budget.ts

@@ -12,11 +12,17 @@ import {
   TOOL_ANNOTATIONS_NON_IDEMPOTENT,
   demoDenied, noAccess, ok,
 } from './_shared';
+import { canWrite } from '../scopes';
+import { isAddonEnabled } from '../../services/adminService';
+import { ADDON_IDS } from '../../addons';
 
-export function registerBudgetTools(server: McpServer, userId: number): void {
+export function registerBudgetTools(server: McpServer, userId: number, scopes: string[] | null): void {
+  const W = canWrite(scopes, 'budget');
+
+  if (isAddonEnabled(ADDON_IDS.BUDGET)) {
   // --- BUDGET ---
 
-  server.registerTool(
+  if (W) server.registerTool(
     'create_budget_item',
     {
       description: 'Add a budget/expense item to a trip.',
@@ -38,7 +44,7 @@ export function registerBudgetTools(server: McpServer, userId: number): void {
     }
   );
 
-  server.registerTool(
+  if (W) server.registerTool(
     'delete_budget_item',
     {
       description: 'Delete a budget item from a trip.',
@@ -60,7 +66,7 @@ export function registerBudgetTools(server: McpServer, userId: number): void {
 
   // --- BUDGET (update) ---
 
-  server.registerTool(
+  if (W) server.registerTool(
     'update_budget_item',
     {
       description: 'Update an existing budget/expense item in a trip.',
@@ -88,7 +94,7 @@ export function registerBudgetTools(server: McpServer, userId: number): void {
 
   // --- BUDGET ADVANCED ---
 
-  server.registerTool(
+  if (W) server.registerTool(
     'set_budget_item_members',
     {
       description: 'Set which trip members are splitting a budget item (replaces current member list).',
@@ -108,7 +114,7 @@ export function registerBudgetTools(server: McpServer, userId: number): void {
     }
   );
 
-  server.registerTool(
+  if (W) server.registerTool(
     'toggle_budget_member_paid',
     {
       description: 'Mark or unmark a member as having paid their share of a budget item.',
@@ -128,4 +134,5 @@ export function registerBudgetTools(server: McpServer, userId: number): void {
       return ok({ member });
     }
   );
+  } // isAddonEnabled(BUDGET)
 }