Fix web UI chat refresh and PTY submit

[edwin-zvs]

Summary

• reload chat transcript panes when returning from terminal mode so messages that arrived while terminal was active are visible
• mark cached offscreen chat panes stale when renderable transcript events arrive
• send PTY composer text and Enter as separate inputs so Codex submits instead of treating the combined text+newline as inserted prompt text

Testing

• git diff --check
• cargo test -p agentd
• cargo build