feature(web/monitor): Triggers tab UI

[jamby77]

Summary

PR 17 of the MONITOR stack. Adds the Pro+ Triggers tab to `/monitor`.

• New `TriggersTable` component renders: created at, status badge (`configured` / `queued` / `fired` / `skipped` / `expired` / `cancelled`), source anomaly (`metricType / anomalyType`), expiry (relative), fired session id (short), created by, and a Delete button on active rows
• `Monitor.tsx` wraps the existing sessions table in a Tabs container; the Triggers tab is visible only when the license grants `Feature.MONITOR_ANOMALY_TRIGGER` (Pro+)
• `monitorApi` gains `listTriggers` / `createTrigger` / `cancelTrigger`
• Triggers list polls every 5 s; `cancelTrigger` invalidates the query so the row disappears on success
• Picked up the two new webhook event labels (`monitor.session.skipped`, `monitor.trigger.created`) introduced in PR 16 so they render correctly in `WebhookForm`

How to verify

Requires a Pro+ license configured locally (otherwise the API returns 402 and the tab is hidden).

1. `MONITOR_DEV_PREVIEW=true VITE_MONITOR_DEV_PREVIEW=true pnpm dev` with a Pro+ license loaded.
2. `curl -X POST localhost:3001/monitor/triggers -d '{"connectionId":"","metricType":"connections","anomalyType":"spike"}'` (from PR 15).
3. Browser → `/monitor` → click the Triggers tab. The created trigger appears with `status: configured`.
4. Click Delete → row disappears within one poll; `curl /monitor/triggers` returns `[]`.

Test plan

• `pnpm exec tsc --noEmit` (apps/web) → clean
• `pnpm exec eslint` on touched files → clean
• `pnpm exec vitest run` (apps/web) → 187 tests pass
• Verified API gate: GET `/monitor/triggers` returns 402 on Community tier (`feature: monitorAnomalyTrigger`)
• Live verify the Triggers tab renders + delete works on a Pro+ license (deferred — no Pro license configured locally)