fix: Complete Keycloak external IdP integration with all tests passing

This commit completes the Keycloak external IdP integration for the MCP
server, implementing ADR-002 Tier 2 (External Identity Provider) with
full Bearer token authentication support.

Key Changes:
1. **Keycloak backchannel-dynamic configuration**
   - Added --hostname-strict=false and --hostname-backchannel-dynamic=true
   - Allows external issuer (localhost:8888) with internal endpoints (keycloak:8080)
   - Solves Docker networking issue where containers can't reach localhost

2. **CORSMiddleware Bearer token patch**
   - Created app-hooks/patches/cors-bearer-token.patch from upstream commit 8fb5e77db82
   - Allows Bearer tokens to bypass CORS/CSRF checks (stateless authentication)
   - Applied via post-installation hook 20-apply-cors-bearer-token-patch.sh
   - Enables app-specific APIs (Notes, Calendar, etc.) to work with Bearer tokens

3. **Patch organization**
   - Moved patches to app-hooks/patches/ directory
   - Updated docker-compose.yml to mount entire app-hooks directory
   - Consolidated patch management for better maintainability

4. **Test improvements**
   - All 11 Keycloak integration tests passing
   - Tests validate OAuth token acquisition, MCP connectivity, token validation,
     tool execution, token persistence, user provisioning, scope filtering,
     and error handling

Architecture:
- Keycloak acts as external OAuth/OIDC identity provider
- MCP server uses Keycloak tokens to access Nextcloud APIs
- Nextcloud user_oidc app validates Bearer tokens from Keycloak
- No admin credentials needed - all API access uses user's OAuth tokens

Cache Note:
- Discovery and JWKS caches must be cleared when switching Keycloak configurations
- Use: docker compose exec redis redis-cli DEL "<cache-key>"
- Or: docker compose exec app php occ user_oidc:provider keycloak --clientid nextcloud

Related:
- ADR-002: Vector sync background jobs authentication
- Validates external IdP integration pattern
- Demonstrates offline_access with refresh tokens (Tier 1 & 2)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

env.sample

@@ -8,12 +8,19 @@ NEXTCLOUD_HOST=
 # - Requires Nextcloud OIDC app installed and configured
 # - Admin must enable "Dynamic Client Registration" in OIDC app settings
 # - Leave NEXTCLOUD_USERNAME and NEXTCLOUD_PASSWORD empty to use OAuth mode
+# - OAuth client credentials are stored encrypted in SQLite (TOKEN_STORAGE_DB)
 # - Optional: Pre-register client and provide credentials (otherwise auto-registers)
 NEXTCLOUD_OIDC_CLIENT_ID=
 NEXTCLOUD_OIDC_CLIENT_SECRET=
-NEXTCLOUD_OIDC_CLIENT_STORAGE=.nextcloud_oauth_client.json
 NEXTCLOUD_MCP_SERVER_URL=http://localhost:8000
 
+# OAuth Storage Configuration (SQLite storage for OAuth clients and refresh tokens)
+# TOKEN_ENCRYPTION_KEY: Required for encrypting OAuth client secrets and refresh tokens
+# Generate with: python -c "from cryptography.fernet import Fernet; print(Fernet.generate_key().decode())"
+#TOKEN_ENCRYPTION_KEY=
+# TOKEN_STORAGE_DB: Path to SQLite database (default: /app/data/tokens.db)
+#TOKEN_STORAGE_DB=/app/data/tokens.db
+
 # Option 2: Basic Authentication (LEGACY - Less Secure)
 # - Requires username and password
 # - Credentials stored in environment variables