feat: add window management (merge + labels)

[GindaChen]

Summary

• Merge windows button consolidates all Chrome windows into the current one with a single click
• Show/Hide windows toggle labels each tab with its window of origin (Window 1, Window 2, etc.)
• Window count displayed in the footer stats alongside the existing tab count

Why

Users with tabs spread across multiple Chrome windows have no easy way to see which tab lives where, or to consolidate everything when context-switching. This is especially useful when you've accumulated windows throughout the day and want to clean up without losing tabs.

What's included

• JS (~75 lines):
  • buildWindowNameMap() assigns sequential names to each unique windowId
  • getWindowCount() returns the number of distinct windows
  • mergeAllWindows() moves all tabs into the current window via chrome.tabs.move()
  • showWindowLabels toggle state and re-render logic
  • Two new event handlers (merge-windows, toggle-window-labels) in the existing delegation listener
• HTML: one additional <div class="stat"> in the footer for window count
• CSS (~13 lines): .chip-window-badge style using the existing --accent-slate token

How it works

1. On render, buildWindowNameMap() maps each windowId → "Window 1", "Window 2", etc.
2. If 2+ windows exist, two buttons appear in the section header:
   • "Merge N windows" — calls chrome.tabs.move() for every tab not in the current window, then re-renders
   • "Show windows" — toggles showWindowLabels, which adds a small slate-blue badge to each tab chip
3. After merging, only 1 window remains → both buttons auto-hide on next render
4. Footer shows the live window count

Test plan

• With 1 window open: verify no merge button or window toggle appears (clean UI)
• Open 2+ Chrome windows, reload Tab Out: verify "Merge N windows" and "Show windows" buttons appear
• Click "Show windows" — verify each tab chip shows a "Window 1" / "Window 2" badge
• Click "Hide windows" — verify badges disappear
• Click "Merge N windows" — verify all tabs move to the current window, other windows close
• After merge, verify buttons disappear and footer shows "1" window
• Verify footer window count updates correctly as windows open/close

🤖 Generated with Claude Code