Add telemetry batch flush tests

[xxCodexIAxx]

Summary

• Adds focused telemetry batch flush coverage for the 100-event threshold.
• Verifies page unload flushing, partial batch preservation, and reset of queued/retry state after a successful flush.
• Adds a test:telemetry npm script and documents the focused validation command in operations docs.

Changes

• Exported small test-only helpers from frontend/src/services/telemetry.ts so the batch queue can be reset, inspected, and flushed deterministically.
• Added frontend/scripts/test-telemetry-batch-flush.mjs using Node's built-in test runner with browser API stubs.
• Added npm run test:telemetry.
• Documented the telemetry batch validation flow in docs/OPERATIONS.md.

Testing

• Syntax checked the new test script with node --check frontend/scripts/test-telemetry-batch-flush.mjs.
• Intended focused test: cd frontend && npm run test:telemetry.
• Intended full validation: python3 build.py.
• I did not run repository code locally because this environment blocks executing code from downloaded public repositories.

Bounty

Fixes #10.

Payout wallet: 0x776CbBb63D81c08B4090DB503eAE7FDb8fBd7c6f