feat: add WebDriver BiDi transport and normalized health events

[llmxtfai]

Summary

• add a protocol-neutral browser transport with Edge/CDP and Firefox/WebDriver BiDi adapters
• normalize browser health observations behind the versioned health_events_v2 contract
• preserve current-tab actions, input, screenshots, navigation, and clean shutdown across both engines
• bump the proposed package version to 0.2.0

Why

Angel3 reproduced Firefox-only Tactical failures that Edge-only automation did not catch. This provides the cross-engine transport needed to run the same functional contract in both browsers without introducing a second test runner.

Verification

• 108 Python tests pass
• focused Ruff checks pass
• real visible Edge and Firefox interaction exercises pass
• Firefox Tactical production proof held the same document and canvas for more than four minutes without reload or WebGL loss

Integration note

This branch also contains the sequenced browser-health foundation required by the normalized event contract. Upstream main advanced during the incident work, so this is opened as a draft while the current-main integration is reconciled.

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Summary by cubic

Add a protocol-neutral browser transport with adapters for Edge/CDP and Firefox/WebDriver BiDi to run the same actions in both engines. Normalize and sequence browser health observations under the versioned health_events_v2 contract, and expose a live capability manifest.

• New Features

  • Add WebDriver BiDi transport for Firefox; default remains CDP for Edge. Select via BU_BROWSER_PROTOCOL=bidi with BU_BIDI_URL and BU_BIDI_CONNECT_HOST.
  • Keep cross-engine parity for current-tab actions, input, screenshots, navigation, and clean shutdown.
  • Introduce health_events_v2 with begin, events_since, and seal, plus schema attestation.
  • Add helpers: health_capabilities(), health_begin(), health_events_since(), health_seal(), and browser_capabilities(). New CLI: browser-harness --capabilities prints live JSON.
  • Bump browser-harness to 0.2.0.

• Migration

  • Move to the health_events_v2 helpers; v1 is superseded.
  • To use Firefox via BiDi, set BU_BROWSER_PROTOCOL=bidi and provide BU_BIDI_URL and BU_BIDI_CONNECT_HOST. No change needed to stay on Edge/CDP.
  • Detect runtime support with helpers.browser_capabilities() or browser-harness --capabilities.

^{Written for commit 83b591d. Summary will update on new commits.}