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/schemas/run.py

@@ -9,6 +9,7 @@ class RunCreate(CamelModel):
     game_id: int
     name: str
     rules: dict = {}
+    naming_scheme: str | None = None
 
 
 class RunUpdate(CamelModel):
@@ -16,6 +17,7 @@ class RunUpdate(CamelModel):
     status: str | None = None
     rules: dict | None = None
     hof_encounter_ids: list[int] | None = None
+    naming_scheme: str | None = None
 
 
 class RunResponse(CamelModel):
@@ -25,6 +27,7 @@ class RunResponse(CamelModel):
     status: str
     rules: dict
     hof_encounter_ids: list[int] | None = None
+    naming_scheme: str | None = None
     started_at: datetime
     completed_at: datetime | None