feat(recovery): add safe-mode recovery surface and emergency CLI (#1286)

* feat(recovery): add safe-mode recovery surface and emergency CLI

Add a read-only Recovery tab under Settings (admin-only) backed by a new
GET /api/diagnostics endpoint reporting app version, database integrity,
encryption-key status, Docker reachability, account and SSO counts, and
non-secret configuration. The endpoint loads without Docker or live metrics
so it stays available when the dashboard does not, requires a genuine admin
session, and builds its config block from a non-secret allowlist so no
credentials are ever exposed.

Expand the emergency command-line toolkit beyond the two-factor reset with
seven host-level commands: reset-password, create-emergency-admin,
clear-sessions, disable-sso, diagnostics, validate-db, and backup-data. Each
prints its result, exits with a meaningful status code, and writes an audit
entry where it changes state.

Document the toolkit in a new operator guide and link it from the recovery
and two-factor pages.

* feat(recovery): download the emergency command reference as a text file

The recovery commands are needed exactly when the dashboard is unreachable,
so reading them only in-app is a chicken-and-egg problem. Add a Download
button to the command-line section that saves the full
`docker compose exec sencho ...` reference as a text file, letting operators
keep it on hand before they need it. Reuses a shared download helper with the
existing diagnostics export.

* fix(recovery): harden diagnostics, backup, and emergency-admin against edge cases

Address findings from an independent review of the recovery toolkit:

- DiagnosticsService now degrades instead of throwing when a queried table is
  missing or corrupt: each read falls back and is folded into database.ok, so a
  broken database reports "problem detected" rather than failing the whole
  endpoint or showing a misleading healthy state with zeroed counts.
- backup-data refuses a destination that resolves to the live database, which
  would otherwise report success while producing no separate copy.
- create-emergency-admin now applies the same username rule as the user-
  management route, extracted to a shared helper so both stay in sync.

Adds tests for a missing read table, a malformed emergency-admin username, and
the backup same-target rejection.

backend/src/routes/diagnostics.ts

@@ -0,0 +1,38 @@
+import { Router, type Request, type Response } from 'express';
+import { requireAdmin, requireUserSession } from '../middleware/tierGates';
+import { collectDiagnostics } from '../services/DiagnosticsService';
+import DockerController from '../services/DockerController';
+import { withTimeout } from '../utils/withTimeout';
+
+export const diagnosticsRouter = Router();
+
+const DOCKER_PING_TIMEOUT_MS = 2000;
+
+// Recovery diagnostics for the local control plane. Restricted to a genuine
+// signed-in admin session: requireUserSession rejects API tokens and
+// node_proxy / pilot_tunnel machine credentials so a long-lived machine token
+// cannot read the control plane's configuration inventory. Read-only and
+// secret-free (see DiagnosticsService for the redaction allowlist). The Docker
+// probe is bounded and wrapped so a down or hung daemon yields
+// `docker.reachable: false` instead of failing the whole request, which is the
+// exact condition an operator opens this surface to diagnose.
+diagnosticsRouter.get('/', async (req: Request, res: Response): Promise<void> => {
+    if (!requireUserSession(req, res)) return;
+    if (!requireAdmin(req, res)) return;
+    try {
+        const report = await collectDiagnostics({
+            checkDocker: async () => {
+                await withTimeout(
+                    DockerController.getInstance().getDocker().ping(),
+                    DOCKER_PING_TIMEOUT_MS,
+                    'docker-ping',
+                );
+                return true;
+            },
+        });
+        res.json(report);
+    } catch (err) {
+        console.error('[diagnostics] failed to collect report:', (err as Error).message);
+        res.status(500).json({ error: 'Failed to collect diagnostics.' });
+    }
+});