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/migrations.py

@@ -11,6 +11,7 @@ from pathlib import Path
 
 from alembic.config import Config
 
+import nextcloud_mcp_server.alembic as alembic_package
 from alembic import command
 
 logger = logging.getLogger(__name__)
@@ -30,8 +31,6 @@ def get_alembic_config(database_path: str | Path | None = None) -> Config:
     Returns:
         Alembic Config object configured for the specified database
     """
-    from nextcloud_mcp_server import alembic as alembic_package
-
     # Use package location (works in both editable and installed modes)
     if alembic_package.__file__ is None:
         raise RuntimeError("alembic package __file__ is None")