feat(editor): click to position the comment cursor

[emo-eth]

Summary

• enable button-only mouse capture in the full and Rust Lite editors
• move the comment cursor on left-click across wrapping, scrolling, blank lines, wide text, and grapheme clusters
• consume SGR and legacy mouse reports without leaking malformed input into comments
• keep TypeScript and Rust terminal layout behavior in parity

Verification

• bun test — 78 passed
• bun run typecheck
• cargo +1.96.1 test --manifest-path rust/Cargo.toml — 72 passed
• cargo +1.96.1 fmt --manifest-path rust/Cargo.toml --check
• rustup run 1.96.1 bash scripts/parity-lite.sh — 407 observables, 95 screens, zero divergences / 1 deliberate
• exercised click-to-position through an actual Herdr popup in both full and Rust Lite runtimes