Add critical browser UX coverage

[chudodey]

What changed

• added append-only Wheel events with optional inline context notes and standalone insights
• connected high-confidence background classification to an already fixed daily Plan with an explainable reason
• added five real-browser Playwright flows for capture, Plan, Tree, Wheel, and Future
• isolated every browser test in a disposable vault with deterministic local-AI responses
• added a one-command local runner and a dedicated Chromium CI job
• marked WHEEL-001 and TECH-001 complete in the machine-readable backlog

Why

The browser layer had no end-to-end protection, and the requested wheel note flow did not exist yet. The implementation now protects the core monthly-use UX without reading or mutating the personal data/ vault.

Validation

• pytest -q — 129 passed, 1 skipped
• python scripts/run_e2e.py --skip-browser-install — 5 passed
• ruff check src tests e2e scripts main.py
• node --check web/static/app.js
• python scripts/backlog.py --check