refactor: enforce PLC0415 (import-outside-top-level) for source code

Enable ruff PLC0415 rule for all source files (tests excluded via
per-file-ignores). Move 136 inline imports to top-level across 33 files.
8 imports suppressed with noqa for legitimate reasons: circular
dependencies (client/__init__.py, context.py), optional dependency
guards (app.py document processors, auth/userinfo_routes.py), and
post-env-setup imports (smithery_main.py).

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

nextcloud_mcp_server/auth/client_registry.py

@@ -10,6 +10,7 @@ import logging
 import os
 from dataclasses import dataclass
 from typing import Dict, List, Optional
+from urllib.parse import urlparse
 
 logger = logging.getLogger(__name__)
 
@@ -161,8 +162,6 @@ class ClientRegistry:
             True if valid, False otherwise
         """
         # Parse the redirect URI
-        from urllib.parse import urlparse
-
         parsed = urlparse(redirect_uri)
 
         # Check against registered patterns