Refit embedded terminals when windows regain focus

[luckeyfaraday]

Summary

• refit and refresh active embedded terminals when the Electron window regains focus or visibility
• reset the cached terminal size so PTY resize/SIGWINCH is resent after window restoration
• keep the fix scoped to the React terminal mount, without CSS overrides or resize-event churn

Risk checks

• reviewed prior terminal fixes Fix terminal repaint after workspace tab switches #146, Warn before launching agents onto a memory-starved machine #181/#output ack recovery, and renderer refresh churn changes
• removed an earlier helper-textarea CSS clamp because it could interfere with xterm IME composition
• this does not call terminal.focus(), so it should not steal focus between panes or controls

Verification

• npm run build
• npm run test:electron
• npm run test:chat
• git diff --check

Manual smoke still recommended

• open two terminal panes, switch away and back to Athena, verify both redraw
• verify typing still goes to the previously focused pane
• verify workspace tab switching still redraws TUI output