(MOT-4443) fix(console): recover router presence after reconnect

[ytallo]

Summary

• re-probe llm-router presence whenever the browser reconnects, including when the router was previously absent
• track router worker identity and revision so a router restart rebuilds provider/catalog subscriptions even when presence stays true
• discard stale presence, provider, and catalog responses from superseded probes
• make the model refresh action authoritatively re-check router presence before refreshing providers and the catalog
• add focused presence-watcher coverage and provider-backed quickstart scenarios for router restart and browser WebSocket outage recovery

Root cause

The Console could miss the router arrival event while its browser WebSocket was disconnected. Because the presence watcher remained absent, the model picker stayed disabled after reconnecting. A present-to-present router replacement also kept the same boolean state, so router-owned subscriptions were not necessarily rebuilt.

Impact

The model picker can recover without reloading the page when the router starts during a browser connection outage or when the router process is replaced. Transient fetch failures preserve the last confirmed catalog while successful empty responses still clear it.

Testing

• pnpm test: 1,213 tests passed
• pnpm run typecheck
• pnpm run typecheck:e2e
• Console production build
• Biome on touched Console and Playwright files
• bash -n harness/tests/quickstart/run-ci.sh
• git diff --check
• Playwright quickstart discovery lists both new recovery scenarios

The provider-backed quickstart scenarios were not executed end-to-end because they require a dedicated live stack and provider credentials.

Stacked on #808 and targets its head branch.

Refs MOT-4443

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