feat: cross-window refresh sync, tray menu & UI improvements

[shixy96]

Summary

🔄 Refresh State Synchronization

• Add refresh-started/refresh-completed events for cross-window state sync
• Create useRefreshState hook to keep refresh button states in sync between Dashboard and Tray windows

🖱️ Tray Context Menu

• Add right-click context menu with Dashboard, Settings, and Quit options
• Rename dashboard window label to main for consistency

📊 Cache Token Statistics

• Add cacheCreationInputTokens and cacheReadInputTokens fields to DailyUsage type
• Display period-aggregated cache tokens in Dashboard stats (instead of today-only)

✨ UI Polish

• Improve Dashboard chart with gradient fill for token bars
• Refactor model breakdown layout with better pie chart proportions
• Extract createNumberInputHandlers helper in Settings for cleaner code
• Adjust glass effect opacity for better visibility
• Polish Tray UI spacing and progress bar layout

🔧 CI/CD

• Add build-test.yml workflow for PR validation on macOS
• Install create-dmg in release workflow for macOS DMG builds

Test Plan

• Click refresh in Dashboard, verify Tray refresh button also shows spinning state
• Click refresh in Tray, verify Dashboard refresh button also shows spinning state
• Right-click tray icon, verify context menu shows Dashboard, Settings, Quit
• Click Dashboard menu item, verify main window opens to dashboard tab
• Click Settings menu item, verify main window opens to settings tab
• Click Quit menu item, verify app exits
• Verify cache token stats update correctly when switching time range (7d/30d)
• Create a PR and verify build-test workflow runs successfully