Align extension UI and verification lifecycle with spec model

[jt55401]

Implement the browser-extension cleanup from the spec review.

Tasks:

• Consume the updated browser-client verifier and protocol model.
• Treat server-HTML snapshot verification as source verification unless the rendered DOM still matches the verified snapshot.
• Avoid displaying a simple valid rendered-content badge when live DOM has diverged.
• Move detailed debug logging behind an explicit developer setting and redact content/key material by default.
• Make page-DOM badges clearly secondary to the extension popup or another less-spoofable surface.
• Align key/directory fetch behavior with the provisional network/CSP/privacy model.

Spec tracking issue: HTMLTrust/htmltrust-spec protocol cleanup after security review.