feat(browser): add in-app page annotations

[arnestrickmann]

Summary

• add task-scoped browser annotation capture, storage, overlay UI, and toolbar controls
• add browser annotation context actions that paste into the active terminal and optionally submit
• add shared annotation formatting plus focused tests for capture, store, toolbar, context action, and terminal assignment behavior
• add local package Vitest configs and test isolation fixes needed for the suite to run from this worktree

Validation

• pnpm run format: passed
• pnpm run lint: passed with existing warnings
• pnpm run typecheck: passed
• focused annotation tests: passed, 7 files / 31 tests
• pnpm run test: app/package tests pass except browser-project startup on this host; fallback Chromium installs with PLAYWRIGHT_HOST_PLATFORM_OVERRIDE=ubuntu24.04-x64 but cannot launch because sudo-only system libraries such as libatk-1.0.so.0 and X11/GTK/audio dependencies are missing

Notes

• Computed styles are intentionally left out of v1.
• Annotation assignment reuses the existing task context and PTY prompt-injection path rather than adding a parallel send flow.