chore: remove the code the legacy CSV importer left behind

`backend/migration.py` and `scripts/migrate_csv_to_db.py` import `School`,
`SchoolResult`, `init_db` and `set_db_schema_version` — names that no longer
exist. `scripts/geocode_schools.py` imports the same removed ORM model. None of
the three can be imported against the current backend, so they were not dormant
utilities anyone could fall back on; they were files that would fail on the
first line. `backend/version.py` existed only to hand `SCHEMA_VERSION` to that
importer, and the FastAPI lifespan performs no version-triggered import.

Three symbols go with them, each confirmed to have no caller: the unvectorised
`haversine_distance`, superseded by the inline NumPy calculation in search;
`fetcher`, an SWR helper for a dependency this project does not install; and
`kmToMiles`. `calculateDistance` stays — CutoffMapPanel uses it.

Two comments pointed at `migrate_csv_to_db.py --drop` to explain why Payload
owns its own schema. The reason survives the script: blog content must stay
clear of the school marts and Airflow's metadata. Reworded rather than deleted,
so the constraint keeps its justification.

docs/LEGACY_CODE.md records what was removed and where to find it in history. It
also records what was deliberately *not* removed, which is the more useful half:
unused UI components awaiting a design decision, manual data utilities whose
operators a repository search cannot see, and fallbacks that look obsolete but
are load-bearing — `data_loader.py`'s older-mart branches, the generated GIAS
dictionary copies, and the `legacy`-named dbt models that annual DAG selectors
explicitly include. A zero-import count is evidence, not a verdict.

The scripts that fetch DfE CSVs are marked historical and kept, pending
confirmation that nobody runs them by hand.

Checked: 190 backend tests, 429 frontend tests, `tsc --noEmit` clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016y2J6bs8gbuSJbH18w7Tan

nextjs-app/__tests__/payload/routes.test.ts

@@ -38,8 +38,7 @@ describe('payload mount points', () => {
   });
 
   it('isolates CMS tables in their own postgres schema', () => {
-    // Blog content must sit outside `public`, where the app tables, Airflow's
-    // metadata and scripts/migrate_csv_to_db.py --drop all live.
+    // Blog content must stay separate from school marts and Airflow metadata.
     expect(CONFIG).toMatch(/schemaName:\s*['"]payload['"]/);
   });
 });

nextjs-app/lib/api.ts

@@ -311,26 +311,6 @@ export async function fetchDataInfo(
   return handleResponse<DataInfoResponse>(response);
 }
 
-// ============================================================================
-// Client-Side Fetcher (for SWR)
-// ============================================================================
-
-/**
- * Generic fetcher function for use with SWR
- * @example
- * ```tsx
- * const { data, error } = useSWR('/api/schools', fetcher);
- * ```
- */
-export async function fetcher<T>(url: string): Promise<T> {
-  // If it's already a full URL, use it directly
-  // Otherwise, prepend the API_BASE_URL
-  const fullUrl = url.startsWith('http') ? url : `${API_BASE_URL}${url.startsWith('/') ? url : `/${url}`}`;
-
-  const response = await fetch(fullUrl);
-  return handleResponse<T>(response);
-}
-
 // ============================================================================
 // Geocoding API
 // ============================================================================
@@ -396,10 +376,3 @@ export function calculateDistance(
   const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
   return R * c;
 }
-
-/**
- * Convert kilometers to miles
- */
-export function kmToMiles(km: number): number {
-  return km * 0.621371;
-}

nextjs-app/payload.config.ts

@@ -24,9 +24,8 @@ export default buildConfig({
   typescript: { outputFile: path.resolve(dirname, 'payload-types.ts') },
   db: postgresAdapter({
     pool: { connectionString: process.env.DATABASE_URL },
-    // Its own schema, so no pipeline operation on `public` can reach blog
-    // content. scripts/migrate_csv_to_db.py --drop lives in that blast radius,
-    // as does Airflow's metadata. The schema itself is created by the initial
+    // Its own schema separates blog content from pipeline-managed school
+    // tables and Airflow metadata. The schema is created by the initial
     // migration: schemaName says where tables go, it does not create anything.
     //
     // prodMigrations runs pending migrations during server init. Without it a