Add web UI PTY view toggle

[edwin-zvs]

Summary

• add a Terminal/Chat segmented toggle for selected PTY-capable web UI sessions
• keep terminal view as the default and remember explicit per-session web view preferences
• skip raw PTY byte streams in chat mode so ANSI repaint/status output does not appear as transcript text
• mirror native interactive transcripts from Codex, Claude, and Antigravity into semantic agentd events for chat mode
• document the UX rule in a web UI spec

Testing

• rustfmt --edition 2024 --check crates/adapter-codex/src/main.rs crates/adapter-claude/src/main.rs crates/adapter-antigravity/src/main.rs
• git diff --check
• cargo check
• cargo test -p agentd-adapter-codex
• cargo build