Refactor transit_api into a repo/routes module split

Split the 5,441-line index.js into an 86-line bootstrap, thin domain
route modules, shared lib/ helpers, and a repo/ layer that isolates the
DEV_MOCK branches (repo/*.mock.js). Repo methods return {statusCode, body};
routes are one-line wrappers. Pin search_path to "transit.bus" and
document the /bus/ prefix with legacy root aliases (Deprecation header).

Parity verified: 57/57 byte-identical on the stub differential harness
plus 24/24 live read-only responses vs the original against real
PostgreSQL. The only intentional behavior change: mock reorder/delete
bus-line endpoints no longer require a live DB (previously 500 in
DEV_MOCK=1 without PG). DEV_MOCK gate and node --check clean.

transit_api/repo/drivers.mock.js

@@ -0,0 +1,34 @@
+const { store } = require("../mock/store");
+const { checkDriverConflict } = require("../lib/schedule");
+const { reportError } = require("../lib/report-error");
+
+// Driver repository methods (DEV_MOCK mode).
+
+async function listDrivers(req) {
+  try {
+    const drivers = store.drivers
+      .slice()
+      .filter((d) => d.status === "active");
+    return {
+      statusCode: 200,
+      body: {
+        drivers: drivers.map((d) => ({
+          ...d,
+          available: !checkDriverConflict(
+            d.id,
+            new Date().toISOString(),
+            new Date(Date.now() + 24 * 60 * 60 * 1000).toISOString(),
+            [],
+            store.schedules || [],
+          ),
+        })),
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+module.exports = { listDrivers };