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/alembic/versions/e5f6a7b8c9d1_add_naming_scheme_to_nuzlocke_runs.py

@@ -0,0 +1,29 @@
+"""add naming_scheme to nuzlocke_runs
+
+Revision ID: e5f6a7b8c9d1
+Revises: d4e5f6a7b9c0
+Create Date: 2026-02-11 12:00:00.000000
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "e5f6a7b8c9d1"
+down_revision: str | Sequence[str] | None = "d4e5f6a7b9c0"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "nuzlocke_runs",
+        sa.Column("naming_scheme", sa.String(50), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("nuzlocke_runs", "naming_scheme")