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/vector/qdrant_client.py

@@ -6,6 +6,7 @@ from qdrant_client import AsyncQdrantClient, models
 from qdrant_client.models import Distance, VectorParams
 
 from nextcloud_mcp_server.config import get_settings
+from nextcloud_mcp_server.embedding import get_embedding_service
 
 logger = logging.getLogger(__name__)
 
@@ -62,9 +63,6 @@ async def get_qdrant_client() -> AsyncQdrantClient:
         # Get collection name (auto-generated from deployment ID + model)
         collection_name = settings.get_collection_name()
 
-        # Import here to avoid circular dependency
-        from nextcloud_mcp_server.embedding import get_embedding_service
-
         embedding_service = get_embedding_service()
 
         # Detect dimension dynamically (for OllamaEmbeddingProvider)