Add a capability-aware debugger target picker

[bjdodson-openai]

Description

Adds accessible target selection and capability-aware panel state to the top-level debugger.

• Switches only by opaque registry ID and never silently chooses an ambiguous target.
• Keeps unavailable and waiting targets visible with truthful capability state.
• Generation-isolates every asynchronous panel surface during target changes.

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: Focused picker 50/50 and full CLI 395/395 passed; build, strict TypeScript, lint, format, browser syntax, diff, and query checks 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 18/22. Stacked on #170 (bjd/debugger-target-registry). Review this PR as the single incremental commit 54780706 against that base; do not merge it before its parent.

[github-actions]

📊 PR Size: size/XL

Total changes: 2047 lines (5 files)

Top files changed:

• npm_modules/cli/src/debugger/devtoolsPanel.spec.ts: +1139 -14
• npm_modules/cli/debugger/devtools-panel.js: +697 -94
• npm_modules/cli/debugger/devtools-panel.css: +56 -0
• npm_modules/cli/debugger/devtools-panel.html: +24 -3
• npm_modules/cli/debugger/README.md: +20 -0

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