feat: add browser-based user info page with separate OAuth flow

Implements /user and /user/page endpoints for displaying authenticated
user information in both BasicAuth and OAuth modes.

Key Features:
- Separate browser OAuth flow (/oauth/login, /oauth/login-callback, /oauth/logout)
- Session-based authentication using signed cookies
- Token refresh for persistent sessions
- HTML and JSON user info endpoints
- IdP profile information retrieval

Architecture:
- BasicAuth mode: Always authenticated as configured user
- OAuth mode: Browser-based authorization code flow with refresh tokens
- Session stored in SQLite with encrypted refresh tokens
- Server-side token refresh using internal Docker hostnames

OAuth Flow:
- /oauth/login: Initiates browser OAuth flow
- /oauth/login-callback: Handles IdP callback and stores refresh token
- /oauth/logout: Clears session cookie
- /user: JSON API endpoint (requires authentication)
- /user/page: HTML page endpoint (requires authentication)

DCR Scopes Fix:
- MCP server DCR now only requests basic OIDC scopes (openid profile email offline_access)
- Nextcloud app scopes (notes:read, etc.) are for MCP clients, not the server itself
- PRM endpoint dynamically advertises supported scopes from tool decorators

Files:
- nextcloud_mcp_server/auth/browser_oauth_routes.py: Browser OAuth flow handlers
- nextcloud_mcp_server/auth/session_backend.py: Starlette session authentication
- nextcloud_mcp_server/auth/userinfo_routes.py: User info endpoints with token refresh
- tests/server/auth/test_userinfo_routes.py: Unit tests
- tests/server/oauth/test_userinfo_integration.py: OAuth integration tests

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

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

Dockerfile

@@ -1,7 +1,9 @@
 FROM ghcr.io/astral-sh/uv:0.9.7-python3.11-alpine@sha256:0006b77df7ebf46e68959fdc8d3af9d19f1adfae8c2e7e77907ad257e5d05be4
 
-# Install git (required for caldav dependency from git)
-RUN apk add --no-cache git
+# Install dependencies
+# 1. git (required for caldav dependency from git)
+# 2. sqlite for development with token db
+RUN apk add --no-cache git sqlite
 
 WORKDIR /app