Add statistics dashboard, options page, and keyboard shortcuts

[jbingham17]

Summary

• Background service worker (background.js): Tracks comment statistics across PRs, updates the extension badge with hidden counts, and handles keyboard shortcut commands
• Statistics dashboard (dashboard.html/js): Full-page dashboard with summary cards, conic-gradient pie chart, bar chart for severity distribution, and a per-repository breakdown table with export/reset
• Options page (options.html/js): Advanced settings including auto-collapse mode (collapsible bars instead of full hide), badge toggle, stats tracking toggle, default filter presets, and repo stats management
• Keyboard shortcuts: Alt+Shift+1-4 to toggle each severity level directly from any GitHub PR page
• Updated content script: Supports auto-collapse mode, reports stats to background worker, listens for live options/settings changes via storage.onChanged
• Updated popup: Links to dashboard and options page
• Version bump: 1.0.0 → 2.0.0

Changes

• 5 new files added (background.js, dashboard.html, dashboard.js, options.html, options.js)
• 5 existing files modified (manifest.json, content.js, content.css, popup.html, popup.js)
• +1,245 lines across 10 files

Test plan

• Load extension in Chrome and verify popup shows Dashboard/Options links
• Click Dashboard link and verify the stats page renders with empty state
• Click Options link and verify all toggles and selects work and persist
• Toggle auto-collapse mode and verify filtered comments show collapsible bars instead of being hidden
• Test keyboard shortcuts (Alt+Shift+1-4) on a GitHub PR page
• Verify badge count updates on the extension icon when comments are hidden
• Visit multiple PRs and verify per-repo stats accumulate in the dashboard
• Test export and reset functionality on both dashboard and options pages

🤖 Generated with Claude Code