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/cli/disableSso.ts

@@ -0,0 +1,50 @@
+/**
+ * Emergency CLI: disable a broken SSO/OIDC/LDAP provider so local password
+ * sign-in is reachable again. Used when a misconfigured identity provider
+ * blocks the login screen.
+ *
+ * Run via:
+ *   docker compose exec sencho node dist/cli/disableSso.js [provider]
+ *
+ * With no argument it disables every enabled provider. The stored configuration
+ * is preserved (only the enabled flag is cleared) so it can be fixed and
+ * re-enabled from the UI. Written to the audit log with actor `cli`.
+ */
+import { DatabaseService } from '../services/DatabaseService';
+import { auditCli, exitWith, type CliResult } from './_shared';
+
+export function disableSso(provider?: string): CliResult {
+    const db = DatabaseService.getInstance();
+
+    if (provider) {
+        const config = db.getSSOConfig(provider);
+        if (!config) {
+            return { ok: false, message: `No SSO config found for provider: ${provider}` };
+        }
+        if (config.enabled !== 1) {
+            return { ok: true, message: `SSO provider ${provider} is already disabled.` };
+        }
+        db.upsertSSOConfig(provider, false, config.config_json);
+        auditCli(db, `/cli/disable-sso/${provider}`, `CLI disabled SSO provider ${provider}`);
+        return { ok: true, message: `Disabled SSO provider ${provider}. Its configuration was preserved.` };
+    }
+
+    const enabled = db.getEnabledSSOConfigs();
+    if (enabled.length === 0) {
+        return { ok: true, message: 'No SSO providers are currently enabled.' };
+    }
+    for (const config of enabled) {
+        db.upsertSSOConfig(config.provider, false, config.config_json);
+    }
+    const names = enabled.map(c => c.provider).join(', ');
+    auditCli(db, '/cli/disable-sso', `CLI disabled all SSO providers (${enabled.length})`);
+    return { ok: true, message: `Disabled ${enabled.length} SSO provider(s): ${names}. Configurations were preserved.` };
+}
+
+function main(): void {
+    exitWith(disableSso(process.argv[2]));
+}
+
+if (require.main === module) {
+    main();
+}