refactor: tighten native AppKit ownership boundaries

[arzafran]

What this does

• Moves sidebar resize pointer capture into AppKit so drag and cursor behavior stay stable across terminal and browser content.
• Keeps command palette updates inside its AppKit overlay instead of invalidating the whole window shell.
• Shares one native find-field host across browser and terminal search while preserving focus, IME, and selection behavior.
• Makes review-panel rows lazy and cached, and avoids redundant workspace telemetry and browser progress publications.
• Records the measured gates for future native sidebar and main-window ownership work. This does not attempt a wholesale SwiftUI rewrite.

Review order

1. d822e39047 for the sidebar divider and command-palette lifecycle.
2. b5aed430ec for shared find fields and review rendering.
3. 382398a208 for redundant publication removal.
4. 750f7baa7f for the follow-up ownership plans.

Test plan

• Tagged Debug build: ./scripts/reload.sh --tag appkit-improvements
• git diff --check origin/main...HEAD
• Xcode project plist validation
• Full CI workflow
• Sidebar resize UI suite with video
• Command palette and browser/terminal find focus UI cases with video