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/smithery_main.py

@@ -36,7 +36,7 @@ def main():
     logger.info("Starting Nextcloud MCP Server in Smithery stateless mode")
 
     # Import app after setting environment variables
-    from nextcloud_mcp_server.app import get_app
+    from nextcloud_mcp_server.app import get_app  # noqa: PLC0415
 
     # Create the app with streamable-http transport (required for Smithery)
     app = get_app(transport="streamable-http")