fix(browser): record ChatGPT model selection evidence

[pdurlej]

Summary

• persist ChatGPT browser model-selection evidence in session metadata
• print model evidence in browser run logs and session render output
• warn when a large browser Pro run completes suspiciously quickly, so callers verify evidence before claiming Pro Extended output

Why

Browser sessions currently record the requested model/config, but not the observed ChatGPT picker label. This makes fast GPT-5.5 Pro runs hard to audit: the caller can only say what Oracle requested, not what the UI actually showed.

Testing

• pnpm vitest run tests/browser/pageActions.test.ts tests/browser/modelSelection.test.ts tests/browser/sessionRunner.test.ts tests/cli/sessionRunner.test.ts tests/cli/sessionDisplay.test.ts
• pnpm run build
• pnpm run check
• git diff --check
• pnpm test