Add naming scheme selection to run configuration

Add a nullable naming_scheme column to NuzlockeRun so users can pick a
themed word category for nickname suggestions. Includes Alembic migration,
updated Pydantic schemas, a GET /runs/naming-categories endpoint backed by
a cached dictionary loader, and frontend dropdowns in both the NewRun
creation flow and the RunDashboard for mid-run changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/services/naming.py

@@ -0,0 +1,18 @@
+import json
+from functools import lru_cache
+from pathlib import Path
+
+DICTIONARY_PATH = Path(__file__).resolve().parents[1] / "seeds" / "data" / "name_dictionary.json"
+
+
+@lru_cache(maxsize=1)
+def _load_dictionary() -> dict[str, list[str]]:
+    if not DICTIONARY_PATH.exists():
+        return {}
+    with open(DICTIONARY_PATH) as f:
+        return json.load(f)
+
+
+def get_naming_categories() -> list[str]:
+    """Return sorted list of available naming category names."""
+    return sorted(_load_dictionary().keys())