feat(ui): allow minimizing CLI upgrade modals to run in background

[kessenma]

Summary

• CLI upgrade modals (Codex, Claude, GH, OpenCode) now have a minimize button so upgrades can run in the background
• Minimized upgrades show as a titlebar indicator pill (top-right, next to app update indicator) with spinner, CLI name, and progress
• Indicator auto-clears on completion with a success/error toast
• Blocks message sending for a CLI backend while it's being updated, showing an error toast
• Reinstall mode indicator is clickable to restore the modal

Closes #257

Changes

File	Change
src/store/ui-store.ts	Add MinimizedCliUpdate interface, state, and actions
src/components/titlebar/MinimizedCliUpdate.tsx	New - Titlebar indicator with progress tracking and event listeners
src/components/preferences/CliReinstallModal.tsx	Add onMinimize prop and minimize button during install step
src/components/layout/CliUpdateModal.tsx	Wire minimize handler to store actions
src/components/preferences/CliLoginModal.tsx	Add minimize with PTY-safe cleanup (minimizingRef)
src/components/titlebar/TitleBar.tsx	Render MinimizedCliUpdate in right section
src/components/chat/hooks/useMessageSending.ts	Guard against sending while CLI is updating
docs/developer/auto-updates.md	Document minimize feature, button positioning, CLI guard, restore
docs/developer/notifications.md	Document titlebar indicator pattern

Test plan

• Trigger a CLI update toast (or open update modal from Settings)
• Click Update, then click minimize (Minus icon to the left of X)
• Verify modal closes and pill indicator appears in titlebar
• Verify you can use the app normally while upgrade runs
• Verify success/error toast shows on completion and indicator auto-clears
• Verify normal close (X) on modal still stops the process
• Try sending a message with the updating CLI's backend - should show error toast
• For reinstall mode: click the indicator to restore the modal