feat: move fleets into a first-party plugin

plugins/fleets/backend/index.mjs

@@ -0,0 +1,63 @@
+/**
+ * Fleets - first-party, in-process plugin.
+ *
+ * This plugin runs on the main thread rather than in a worker for the same
+ * reason proxmox and ai do (see src/backend/plugins/first-party.ts): its
+ * execute/transfer routes resolve and connect to many hosts concurrently over
+ * the shared SSH pool via resolveHostById and withConnection, read/write
+ * files over SFTP, and stream a zip archive back for pull requests. None of
+ * that fits the worker ctx -- ctx.hosts is a 13-field read-only view with no
+ * fleets surface at all, and ctx.http.route replies with a single postMessage
+ * value rather than a stream.
+ *
+ * Like proxmox, this plugin does not own a live transport (no WebSocket
+ * server, no dedicated port), so it registers its Express router with the
+ * always-mounted /fleets dispatcher in
+ * src/backend/database/routes/fleet-dispatch.ts instead of getting its own
+ * port.
+ *
+ * routes.ts is what used to be src/backend/database/routes/fleet-routes.ts,
+ * moved here and rewritten from `export default router` into
+ * startFleetsService()/stopFleetsService(), called from
+ * activate()/deactivate() below. The fleets/fleetMembers/fleetInventory
+ * tables and their repositories stay in core (src/backend/database/db/schema.ts,
+ * src/backend/database/repositories/fleet-repository.ts,
+ * fleet-inventory-repository.ts) -- this plugin system has no owned-table
+ * migration mechanism of its own, and these tables carry FKs into core's
+ * hosts/users tables.
+ */
+
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+/**
+ * Loads a module by its path relative to this file's own directory.
+ *
+ * The plugin ships beside dist/backend, so in a built server the compiled
+ * .js for routes.js sits right next to this .mjs, and core modules resolve
+ * via ../../../backend/backend/... from there (dist/plugins/fleets/backend
+ * -> dist/backend/backend). Under vitest/dev nothing imports this plugin
+ * directly (the loader loads in-process plugins with a plain dynamic import,
+ * no tsx loader involved), so the only layout that needs to resolve here is
+ * the built one.
+ */
+async function loadRelative(relativePath) {
+  const here = path.dirname(fileURLToPath(import.meta.url));
+  const target = path.join(here, `${relativePath}.js`);
+  return import(new URL(`file://${target.replace(/\\/g, "/")}`).href);
+}
+
+let routesModule = null;
+
+export async function activate(ctx) {
+  routesModule = await loadRelative("routes");
+  routesModule.startFleetsService();
+  ctx.log.info("Fleets router registered at /fleets");
+}
+
+export async function deactivate() {
+  if (routesModule) {
+    routesModule.stopFleetsService();
+    routesModule = null;
+  }
+}