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/placeholder.py

@@ -21,6 +21,7 @@ import logging
 import time
 import uuid
 
+from qdrant_client import models
 from qdrant_client.models import FieldCondition, Filter, MatchValue, PointStruct
 
 from nextcloud_mcp_server.config import get_settings
@@ -82,8 +83,6 @@ async def write_placeholder_point(
 
         # Create empty sparse vector for placeholders
         # Use models.SparseVector with empty indices/values
-        from qdrant_client import models
-
         empty_sparse = models.SparseVector(indices=[], values=[])
 
         # Generate deterministic point ID