Add the web preview performance panel

[bjdodson-openai]

Description

Adds a generation-safe Performance panel over the preceding bounded capture API.

• Keeps Start, Stop, polling, and completed results bound to one exact target generation.
• Preserves focus and scroll while rejecting stale or ambiguous capture state.
• Cleans up ownership on target changes, aborts, and page lifecycle events.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• Documentation improvement
• Performance optimization
• Test improvement
• Other (new debugger capability)

Testing

• Tests pass locally (bazel test //...)
• Added/updated tests for changes (if applicable)
• Tested on multiple platforms (iOS/Android/Web/macOS as applicable)
• Manual testing performed (describe below)

Testing Details

• Incremental branch: Panel 25/25, combined focused 114/114, full CLI 347/347, production build, TypeScript, lint, format, syntax, and query passed.
• Assembled debugger stack: npm test passed 436/436; the CLI production build passed.
• Focused //src/valdi_modules/src/valdi/web_renderer:test passed.
• bazel query //... passed.
• The broad Valdi suite reproduced the established 12 unrelated failures; all new debugger specs passed.

Checklist

• Code follows project style guidelines
• Documentation updated (if needed)
• No breaking changes (or documented in description)
• Commit messages follow conventional format
• No secrets, API keys, or internal URLs included

Related Issues

Relates to #154

Additional Context

Stack 15/22. Stacked on #167 (bjd/debugger-web-performance-api). Review this PR as the single incremental commit c1d9db42 against that base; do not merge it before its parent.

[github-actions]

📊 PR Size: size/XL

Total changes: 1707 lines (6 files)

Top files changed:

• npm_modules/cli/debugger/devtools-panel.js: +679 -4
• npm_modules/cli/src/debugger/devtoolsPanel.spec.ts: +523 -0
• npm_modules/cli/debugger/devtools-panel.css: +402 -0
• npm_modules/cli/debugger/devtools-panel.html: +63 -4
• docs/docs/performance-tracing.md: +26 -0
• npm_modules/cli/debugger/README.md: +4 -2

_{Size calculated as additions + deletions. Labels: XS (<10), S (<50), M (<250), L (<1000), XL (1000+)}