feat(mcp): OAuth so claude.ai and ChatGPT can connect as connectors

MindSift becomes the OAuth authorization server for its own MCP
endpoint: discovery (RFC 9728/8414), dynamic client registration,
authorization code with PKCE (S256), rotating refresh tokens with reuse
detection. The consent page lives in the app at /oauth/authorize. A
grant is an api_keys entry (kind 'oauth'), so scopes, origin badges,
renaming and revoking work as for keys; tokens are valid for /mcp only.
Unused connections expire after OAUTH_IDLE_DAYS (default 90). Requires
BASE_URL; off in demo mode. Release 0.51.0.

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

frontend/src/lib/apiScopes.ts

@@ -0,0 +1,20 @@
+import { ApiKeyScope } from './types';
+
+// What a key may do. The rights hold for every access alike: curl/REST and MCP for AI agents. The ids of
+// the delivering rights (webhook:…) stay from the time keys could only deliver data.
+export type ScopeGroup = 'tasks' | 'lists' | 'inbox';
+export const SCOPES: { id: ApiKeyScope; label: string; chip: string; hint: string; group: ScopeGroup }[] = [
+  { id: 'tasks:read', label: 'Lesen', chip: 'Aufgaben lesen', hint: 'Aufgabenlisten und Aufgaben lesen, suchen', group: 'tasks' },
+  { id: 'webhook:task', label: 'Anlegen', chip: 'Aufgaben anlegen', hint: 'Nur neue Aufgaben anlegen', group: 'tasks' },
+  { id: 'tasks:write', label: 'Ändern', chip: 'Aufgaben ändern', hint: 'Anlegen, ändern, abhaken und löschen', group: 'tasks' },
+  { id: 'lists:read', label: 'Lesen', chip: 'Listen lesen', hint: 'Listen und ihre Einträge lesen', group: 'lists' },
+  { id: 'webhook:list', label: 'Einträge hinzufügen', chip: 'Listeneinträge hinzufügen', hint: 'Nur neue Einträge hinzufügen', group: 'lists' },
+  { id: 'lists:write', label: 'Ändern', chip: 'Listen ändern', hint: 'Einträge hinzufügen, ändern und abhaken', group: 'lists' },
+  { id: 'webhook:triage', label: 'Inbox füllen', chip: 'Inbox', hint: 'Gedanken in die Inbox einliefern', group: 'inbox' },
+];
+export const SCOPE_GROUPS: [ScopeGroup, string][] = [
+  ['tasks', '📋 Aufgaben'],
+  ['lists', '🛒 Listen'],
+  ['inbox', '📥 Inbox'],
+];
+export const scopeChip = (id: string) => SCOPES.find((s) => s.id === id)?.chip || id;