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/stops.mock.js

@@ -0,0 +1,96 @@
+const { store } = require("../mock/store");
+const { reportError } = require("../lib/report-error");
+
+// Stop repository methods (DEV_MOCK mode). Each mirrors the original handler's
+// `if (DEV_MOCK) { ... }` branch verbatim and returns { statusCode, body }.
+
+async function listStops(req) {
+  try {
+    return {
+      statusCode: 200,
+      body: {
+        stops: store.stops.slice().sort((a, b) => a.id - b.id),
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function createStop(req) {
+  try {
+    const { name, latitude, longitude } = req.body;
+
+    if (!name || latitude === undefined || longitude === undefined) {
+      return { statusCode: 400, body: { error: "missing_required_fields" } };
+    }
+
+    const stop = {
+      id: store.nextStopId++,
+      name,
+      latitude: parseFloat(latitude),
+      longitude: parseFloat(longitude),
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    };
+    store.stops.push(stop);
+    return { statusCode: 201, body: { stop } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function deleteStop(req) {
+  try {
+    const { stopId } = req.params;
+
+    if (!stopId || !Number.isFinite(Number(stopId))) {
+      return { statusCode: 400, body: { error: "invalid_stop_id" } };
+    }
+
+    const index = store.stops.findIndex(
+      (s) => Number(s.id) === Number(stopId),
+    );
+    if (index === -1) {
+      return { statusCode: 404, body: { error: "stop_not_found" } };
+    }
+    const deletedStop = store.stops.splice(index, 1)[0];
+    return { statusCode: 200, body: { success: true, stop: deletedStop } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    if (err.code === "23503") {
+      return { statusCode: 409, body: { error: "foreign_key_violation", message: "This stop is referenced by route_stops" } };
+    }
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function updateStop(req) {
+  try {
+    const { stopId } = req.params;
+    const { name, latitude, longitude } = req.body;
+
+    if (!stopId || !Number.isFinite(Number(stopId))) {
+      return { statusCode: 400, body: { error: "invalid_stop_id" } };
+    }
+
+    const stop = store.stops.find((s) => Number(s.id) === Number(stopId));
+    if (!stop) return { statusCode: 404, body: { error: "stop_not_found" } };
+    if (name !== undefined) stop.name = name;
+    if (latitude !== undefined) stop.latitude = parseFloat(latitude);
+    if (longitude !== undefined) stop.longitude = parseFloat(longitude);
+    stop.updatedAt = new Date().toISOString();
+    return { statusCode: 200, body: { stop } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+module.exports = { listStops, createStop, updateStop, deleteStop };