[$25 BOUNTY] [TypeScript] Add frontend connection teardown regression tests

[Saiaaax]

Summary

Adds regression tests verifying WebSocket connection teardown behavior in the frontend, including socket close, timer cleanup, state transitions, and idempotent disconnect.

Closes #70

Changes

• New: frontend/src/hooks/useWebSocket.teardown.test.ts — 10 regression tests:

  • Closes WebSocket with code 1000 on disconnect
  • Clears reconnect timer on disconnect
  • Clears ping timer on disconnect
  • Clears pong timeout on disconnect
  • Sets connection state to disconnected after teardown
  • Handles teardown with no active connection gracefully
  • Handles teardown with all resources active
  • Reconnect timer does not fire after cleanup
  • Ping interval does not fire after cleanup
  • Pong timeout does not fire after cleanup
  • Multiple rapid disconnect calls are idempotent

• Updated: docs/OPERATIONS.md — Added "Frontend WebSocket Teardown" section with cleanup contract table, known regression risks, and test instructions

Testing

cd frontend && npm test -- --run useWebSocket.teardown

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

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• I would like to request that my diagnostic build log is removed before merging

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Payout address: 0x5253757322092903C2F0a8EfEed592344216CC7E
Diagnostic artifact reference: diagnostic/build-5efbbedb.logd