Add browser websocket capture artifacts

[chubes4]

Summary

• Add generic Playwright websocket capture for browser probe/actions via capture=websocket.
• Write redacted browser-websocket artifacts with connection timestamps, frame counts, byte totals, and summary refs.
• Register websocket artifact metadata and document the capture option.

Tests

• npm run test:browser-artifact-session
• npx tsx scripts/browser-probe-contract-smoke.ts
• npm run build

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Implemented the websocket capture primitive, docs, tests, and verification.