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/__init__.py

@@ -113,7 +113,7 @@ class NextcloudClient:
         Returns:
             NextcloudClient configured with bearer token authentication
         """
-        from ..auth import BearerAuth
+        from ..auth import BearerAuth  # noqa: PLC0415
 
         logger.info(f"Creating NC Client for user '{username}' using OAuth token")
         return cls(base_url=base_url, username=username, auth=BearerAuth(token))