test: webhook UUID resolution + fix sse.test.ts Set regression (#3129)

[Shan7Usmani]

Summary

Adds tests verifying the GitHub webhook POST handler resolves githubLogin to the database UUID before calling sendSSEEvent, and fixes a pre-existing regression in sse.test.ts where the sseConnections registry changed to Map<string, Set> but tests still stored plain controller objects.

Changes

• ** est/webhook-sse-integration.test.ts** (new) — 8 tests covering:
  • Webhook resolves githubLogin → database UUID via markUserMetricsStale
  • sendSSEEvent is called with the resolved UUID, not the raw githubLogin
  • Linked account fallback when primary user not found
  • No SSE event when user lookup returns null
  • Payload includes repo name and timestamp
  • Rejects events when webhook secret is missing or signature is invalid
  • Ignores non-push events
• ** est/sse.test.ts** — Fixed 4 failing tests that stored plain controller objects in sseConnections instead of Set, matching the multi-tab connection support added for [FEAT] : Broken Real-Time SSE Dashboard Updates #3129

Acceptance Criteria (from issue)

• ✅ sseConnections successfully registers the active stream controller when a client connects (covered by existing sse-stream-route.test.ts)
• ✅ Disconnecting removes the controller from sseConnections (covered by existing sse-stream-route.test.ts)
• ✅ Webhook route queries the database to map githubLogin → database UUID (new tests)
• ✅ sendSSEEvent is called with the resolved UUID (new tests)
• ✅ Unit tests verify connection registration, payload routing via database UUIDs, and cleanup on socket close (all covered)

Related

Closes #3129

[github-actions]

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