Fix Shift key propagation and focused-pane Cmd routing

[galz10]

Summary

Fixes terminal key propagation so Shift-modified control keys are delivered correctly, and fixes focused-pane command routing so clipboard shortcuts target the pane the user actually focused.

Details

• Updated GhosttyNativeView keyboard handling to preserve Shift for control-text input paths (for example Shift+Enter and Shift+Tab) while still consuming modifiers for printable text when appropriate.
• Added GhosttyKeyEventTranslator helpers to centralize:
  • consumed modifier calculation by flags + emitted text
  • flagsChanged press/release action derivation from keycode + modifier state
• Updated non-text key emission to use consumed_mods = GHOSTTY_MODS_NONE.
• Updated SessionService.setFocusedPane(sessionID:controllerID) to:
  • mark terminal as the last focused surface
  • synchronize AppKit focus for the selected session (ensurePaneController(...).focus()), improving Cmd+C / Cmd+V / Cmd+A routing in split panes.
• Added tests:
  • ShortcutRegistryTests coverage for consumed-mod behavior and flagsChanged press/release behavior.
  • SessionServiceTests coverage for focused-pane terminal intent updates.

Related Issues

Related to terminal modifier propagation and focused-pane clipboard routing regressions.

How to Validate

1. Run tests:
   • xcodebuild test -project idx0.xcodeproj -scheme idx0 -destination 'platform=macOS' -only-testing:idx0Tests/SessionServiceTests -only-testing:idx0Tests/ShortcutRegistryTests
   • Expected: TEST SUCCEEDED.
2. In the app, create a split-pane terminal session and verify:
   • Shift+Enter and Shift+Tab are delivered reliably to the active terminal.
3. Change pane focus (including via pane UI/sidebar), then verify:
   • Cmd+C, Cmd+V, and Cmd+A apply to the currently focused pane.

Pre-Merge Checklist

• lint-docs check is green
• tests check is green
• maintainability result reviewed (phase 1 report-only)
• Added/updated tests (if needed)
• Updated relevant documentation and README (if needed)
• Noted breaking changes (if any)
• Tested on macOS