feat: add playwright reporter emitting ingest batches

[AKogut]

PR-2 of M1: the primary ingestion source. A Playwright Reporter built on the SDK (#91).

What's included

• FlakemetryReporter implementing the Playwright Reporter interface: onBegin → resolve CI run context, onTestEnd → record each attempt, onEnd → build + deliver the ingest batch
• Status mapping: passed@retry0 → pass, passed@retry>0 → flaky, failed/timedOut/interrupted → fail, skipped → skip
• Retry linkage: attempts of the same test share identity; a retry points at its first attempt's index
• CI context from GitHub Actions env (provider, commit, branch, run id, pr number from the ref), with local fallbacks
• Fail-open delivery: no token/endpoint → delivery is a no-op; an upload error never fails the test process
• FLAKEMETRY_OUTPUT_FILE dumps the batch to disk for inspection
• examples/ with a ready playwright.config.ts + README

Verification

• 12 tests (46 across the workspace): status mapping, suite derivation from describe blocks, env → run context incl. pr number, idempotency key strategy, and a full-lifecycle integration test driving synthetic Playwright events → a contract-valid batch (4 executions, flaky retry linked to its first attempt via retryOfIndex, suites distinguished)
• build / lint / typecheck / test green, format:check clean

Notes

• An in-repo Playwright fixture run collides with vitest in the shared node_modules (both register expect), so the end-to-end path is exercised via the lifecycle driver with real Playwright types; a real run against the docker stack is covered by E2E smoke + one-command demo dataset & GIF #29
• The batch resource carries no project — per the contract (packages/contracts — zod schemas as single source of truth #4) the ingest token determines the project server-side

Closes #14.