Add UDP capture-path attribution

[zrack]

Summary

• measure capture-scoped Linux UDP socket drops and preserve explicit unavailable states elsewhere
• add layered UDP byte accounting, bundle v4 writing, and v3/v4 receiver verification
• stabilize large-session responsiveness and workspace-removal regression gates
• update current-state docs, roadmap, and independent field-proof procedure

Verification

• npm run check
• 297 unit/integration tests
• 52 source Playwright tests across Chromium, Firefox, and WebKit
• 6 unpacked-release Playwright tests with reproducible package bytes

Evidence boundary

No physical field handoff is claimed. The current macOS host had no USB telemetry device or identifiable real UDP telemetry source; docs/field-proofs/2026-08-19-readiness.md records the pending setup.