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/fleet.mock.js

@@ -0,0 +1,102 @@
+const { store } = require("../mock/store");
+const { checkBusConflict } = require("../lib/schedule");
+const { reportError } = require("../lib/report-error");
+
+// Fleet repository methods (DEV_MOCK mode).
+
+async function listFleetBuses(req) {
+  try {
+    const buses = store.fleetBuses.slice().sort((a, b) => a.id - b.id);
+    return {
+      statusCode: 200,
+      body: {
+        buses: buses.map((b) => ({
+          ...b,
+          available: !checkBusConflict(
+            b.id,
+            new Date().toISOString(),
+            new Date(Date.now() + 24 * 60 * 60 * 1000).toISOString(),
+            [],
+            store.schedules || [],
+          ),
+        })),
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function createFleetBus(req) {
+  try {
+    const { name, seatCapacity, licensePlate } = req.body;
+
+    if (!name || seatCapacity === undefined || !licensePlate) {
+      return { statusCode: 400, body: { error: "missing_required_fields" } };
+    }
+
+    const bus = {
+      id: store.nextFleetBusId++,
+      name,
+      seatCapacity: Number(seatCapacity),
+      licensePlate,
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    };
+    store.fleetBuses.push(bus);
+    return { statusCode: 201, body: { bus } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function updateFleetBus(req) {
+  try {
+    const { busId } = req.params;
+    const { name, seatCapacity, licensePlate } = req.body;
+
+    if (!busId || !Number.isFinite(Number(busId))) {
+      return { statusCode: 400, body: { error: "invalid_bus_id" } };
+    }
+
+    const bus = store.fleetBuses.find(
+      (b) => Number(b.id) === Number(busId),
+    );
+    if (!bus) return { statusCode: 404, body: { error: "bus_not_found" } };
+    if (name !== undefined) bus.name = name;
+    if (seatCapacity !== undefined) bus.seatCapacity = Number(seatCapacity);
+    if (licensePlate !== undefined) bus.licensePlate = licensePlate;
+    bus.updatedAt = new Date().toISOString();
+    return { statusCode: 200, body: { bus } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function deleteFleetBus(req) {
+  try {
+    const { busId } = req.params;
+    if (!busId || !Number.isFinite(Number(busId))) {
+      return { statusCode: 400, body: { error: "invalid_bus_id" } };
+    }
+
+    const idx = store.fleetBuses.findIndex(
+      (b) => Number(b.id) === Number(busId),
+    );
+    if (idx === -1) return { statusCode: 404, body: { error: "bus_not_found" } };
+    const deleted = store.fleetBuses.splice(idx, 1)[0];
+    return { statusCode: 200, body: { success: true, bus: deleted } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+module.exports = { listFleetBuses, createFleetBus, updateFleetBus, deleteFleetBus };