feat(desktop-monitor): multi-account pool with failover and cooldown

Add monitor-account-pool to select authorized, non-blocked candidates
for an AI-platform monitor task, classify failover reasons (risk
control, challenge, auth failure, empty/unknown result) and cool the
account down before rotating to the next. Wire runtime-controller to run
monitor tasks through the pool, retrying across accounts and annotating
the result with per-account attempt diagnostics and a failover count.
Expose the pool state via the runtime snapshot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/main/runtime-snapshot.ts

@@ -6,6 +6,7 @@ import { getCircuitBreakerState } from './circuit-breaker'
 import { collectRecoverySnapshot } from './crash-recovery'
 import { getKeepAlivePlan } from './keep-alive'
 import { getLeaseManagerSnapshot } from './lease-manager'
+import { getMonitorAccountPoolSnapshot } from './monitor-account-pool'
 import { getMonitorSchedulerSnapshot } from './monitor-scheduler'
 import { getObservedRequestSnapshot } from './network-observer'
 import { getHiddenPlaywrightSnapshot } from './playwright-cdp'
@@ -206,6 +207,7 @@ function createLiveRuntimeSnapshot(controller: RuntimeControllerSnapshot) {
       circuitBreaker: getCircuitBreakerState(),
       keepAlive: getKeepAlivePlan(),
       leaseManager,
+      monitorAccountPool: getMonitorAccountPoolSnapshot(now),
       rateLimiter,
       recovery: collectRecoverySnapshot(),
       runtimeController: {