Auto-claim without the scheduler, and no claim twice

A payout locks in profit and opens nothing, so stopping the trading no
longer stops it: a claim watcher runs the same claims once a minute while
the scheduler is off (its tick still claims while it runs), and the
dashboard's Auto-claim payouts box turns them off.

From two independent reviews of the claim path:
- A claim holds every further claim on the account until Vest's
  transactions show its WITHDRAW. A sync already out when the claim lands
  (by sync generation, not the clock) no longer writes the pre-claim
  balance back, and a fresh sync follows the claim.
- A withdraw that fails in transit (timeout, reset, 5xx) may have gone in:
  it is recorded as of unknown outcome and holds claims the same way,
  until the transactions show it, or an hour of them shows it didn't.
- claimProfit checks Vest's own account: funded (or instant), and no more
  than the balance above its starting capital.
- A claiming account is marked in flight; runClaims sends the amount it
  re-checked under the mutex.
- The watcher starts before the rest of the init can fail; settings are
  validated before any is written.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/api/settings/route.ts

@@ -3,7 +3,7 @@ import { getSetting, setSetting } from '@/lib/db';
 import { scheduleBackupPush } from '@/lib/backup-sync';
 import { getRequestUserAgent } from '@/lib/request-user-agent';
 
-const VALID_KEYS = ['max_concurrent_accounts', 'tick_interval_seconds', 'master_dashboard_url', 'instance_name', 'trading_hours', 'twocaptcha_api_key', 'twocaptcha_proxy', 'master_backup_token', 'proxy_url'] as const;
+const VALID_KEYS = ['max_concurrent_accounts', 'tick_interval_seconds', 'master_dashboard_url', 'instance_name', 'trading_hours', 'twocaptcha_api_key', 'twocaptcha_proxy', 'master_backup_token', 'proxy_url', 'auto_claim'] as const;
 type SettingKey = typeof VALID_KEYS[number];
 
 export async function GET() {
@@ -25,6 +25,12 @@ export async function PATCH(req: NextRequest) {
     try {
         const body = await req.json() as Partial<Record<SettingKey, string | number>>;
 
+        // Claims run unless it reads exactly 'off' — say so exactly, and
+        // before anything is written.
+        if (body.auto_claim !== undefined && body.auto_claim !== null && body.auto_claim !== 'on' && body.auto_claim !== 'off') {
+            return NextResponse.json({ error: "auto_claim is 'on' or 'off'" }, { status: 400 });
+        }
+
         for (const key of VALID_KEYS) {
             if (key in body) {
                 const raw = body[key];