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/notes.py

@@ -4,6 +4,7 @@ import logging
 from typing import Any, AsyncIterator, Dict, Optional
 
 from .base import BaseNextcloudClient
+from .webdav import WebDAVClient
 
 logger = logging.getLogger(__name__)
 
@@ -157,9 +158,6 @@ class NotesClient(BaseNextcloudClient):
                 f"Category changed from '{old_note.get('category', '')}' to '{category}' - cleaning up old attachment directory"
             )
             try:
-                # Import here to avoid circular imports
-                from .webdav import WebDAVClient
-
                 webdav_client = WebDAVClient(self._client, self.username)
                 await webdav_client.cleanup_old_attachment_directory(
                     note_id=note_id, old_category=old_note.get("category", "")
@@ -204,8 +202,6 @@ class NotesClient(BaseNextcloudClient):
 
         # Clean up attachment directories
         try:
-            from .webdav import WebDAVClient
-
             webdav_client = WebDAVClient(self._client, self.username)
 
             for cat in potential_categories: