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/client/webdav.py

@@ -3,7 +3,9 @@
 import logging
 import mimetypes
 import xml.etree.ElementTree as ET
+from email.utils import parsedate_to_datetime
 from typing import Any, Dict, List, Optional, Tuple
+from urllib.parse import unquote
 
 from httpx import HTTPStatusError
 
@@ -1259,8 +1261,6 @@ class WebDAVClient(BaseNextcloudClient):
                 continue
 
             # Decode href path and extract the file path
-            from urllib.parse import unquote
-
             href_path = unquote(href_elem.text)
             # Remove WebDAV prefix to get user-relative path
             webdav_prefix = f"/remote.php/dav/files/{self.username}/"
@@ -1269,8 +1269,6 @@ class WebDAVClient(BaseNextcloudClient):
             # Parse last modified timestamp
             last_modified_timestamp = None
             if lastmodified_elem is not None and lastmodified_elem.text:
-                from email.utils import parsedate_to_datetime
-
                 try:
                     dt = parsedate_to_datetime(lastmodified_elem.text)
                     last_modified_timestamp = int(dt.timestamp())