feat: esc interrupt, ctrl-c clear/quit, working status inline in transcript

[jbj338033]

Summary

Remaps interrupt from Ctrl+C to Esc, changes Ctrl+C to a clear/quit flow, and moves the working status out of the footer and into the transcript area.

• Esc (streaming): immediately sends Op::Interrupt to cancel generation
• Esc (idle, input present): two-step clear — first press shows "again to clear", second clears the composer
• Ctrl+C: no longer interrupts; first press clears composer and shows "again to quit", second press quits
• Working status: spinner/Working…/elapsed now appears inline at the bottom of the transcript (above the composer) instead of the footer
• Interrupted notice: when a turn is interrupted before any text is streamed, a Notice("interrupted") item is appended to the transcript so the cancellation is always visible

Verification

• cargo test -p goat-tui — passed (85 tests, 0 failed)
• cargo clippy --workspace --all-targets -- -D warnings — passed
• cargo fmt --all — passed