UI: consume v3alpha watch streams for live updates

Parent: #5451
API dependencies: #5478, #5480, #5481, #5482

Summary

Consume AlertService and SilenceService server-streaming watch RPCs so the Mantine UI updates from stored mutations without polling, while honoring the API's bounded, node-local, non-durable semantics.

Stream integration

• Use generated direct Connect clients for WatchAlerts, WatchAlertGroups, and WatchSilences; do not route streams through unary-only Connect-Query abstractions.
• Tie every stream to route, component, and filter lifecycle using AbortSignal cleanup.
• Process initial snapshots, explicit snapshot-complete markers, entered/updated/exited transitions, and monotonic node-local sequence numbers.
• Reconcile stream messages into bounded page/query caches without duplicating resources or corrupting deterministic ordering.
• Show unobtrusive live, reconnecting, and stale/resynchronizing state.
• Keep manual refresh and unary list behavior as a functional fallback.

Resynchronization

On queue overflow, ResourceExhausted, disconnect, cancellation not initiated by navigation, Alertmanager restart, invalid cursor, or reconnection to another HA peer:

1. Mark the affected view stale/reconnecting.
2. Stop applying messages from the old stream.
3. Invalidate the relevant unary/query cache.
4. Establish a new watch and consume a fresh initial snapshot.
5. Resume live state only after the snapshot-complete marker.

Do not promise durable replay or cluster-wide cursor continuity. Do not synthesize UI mutation events for time-only status changes that the watch API explicitly omits; derive time state locally or resnapshot when required.

Browser client-streamed alert ingestion is out of scope. Browser alert submission, if added later, remains unary.

Acceptance criteria

• Alerts, alert groups, and Silences update correctly after stored create/update/delete/expire/replacement events.
• Snapshot-to-watch handoff does not visibly lose or duplicate accepted mutations in supported scenarios.
• Entered, updated, and exited filter transitions modify the correct view.
• Overflow, restart, peer change, invalid cursor, and disconnect always trigger a fresh snapshot rather than silently continuing stale state.
• Live state is not shown until an explicit snapshot-complete marker is received.
• Navigation, filter changes, and repeated reconnects release streams, observers, and cache references.
• Manual refresh/unary operation remains usable when streaming is unavailable.
• Component tests use controllable generated streams; real-server tests cover ordering, overflow, cancellation, reconnect, and route prefixes.

Dependencies and related work

• Alerts UI: #5490.
• Silence UI: #5491.
• Connect request/stream controls and observability: #5478.
• Stored-mutation broker and domain feeds: #5480.
• Alert watch methods: #5481.
• Silence watch method: #5482.
• Automatic refresh request: #524.

Likely code areas

• new stream hooks and cache reducers under ui/mantine-ui/src/data/
• Alerts/Silences live-state integration and indicators
• generated stream test helpers and real-server fixtures