v2.0.1: Add Codex CLI/Desktop installation verifier

- Detects codex CLI (via 'which codex' + --version) and Desktop (via /opt/codex-desktop/start.sh)
- Shows green ✔ or yellow ✘ status bar on main page
- 'Install' button opens guide dialog with install commands
- Desktop/CLI launch buttons disabled when corresponding tool is missing
- Dependency status logged on startup
- _set_busy respects missing-state (won't re-enable disabled buttons)
- Rebuilt .deb as v2.0.1

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Changelog
 
+## v2.0.1 (2026-05-19)
+
+- Added Codex CLI/Desktop installation verifier to main page
+- Green check (✔) when detected, yellow cross (✘) when missing
+- "Install" button next to missing tools opens install guide dialog
+- Desktop/CLI launch buttons disabled with tooltip when tool is missing
+- Dependency status logged on startup
+- Buttons respect missing-state after busy/unbusy cycles
+
 ## v2.0.0 (2026-05-19)
 
 - Initial release: multi-provider Codex Launcher