feat: capture PTY terminal sessions

[konard]

Closes #175. Supplies the reusable terminal-capture layer needed by link-assistant/formal-ai#841 in both JavaScript and Rust.

Reproduction

The previous API only spawned pipe-based commands. It could not assign or resize a PTY, retain scrolled-off terminal states, or emit replay artifacts. The new tests reproduce interactive input, control keys, resize observation, full-screen repaint, scrollback, repeated-state preservation, timeout diagnostics, premature PTY-host exits, and platform-specific terminal shutdown.

Changes

• run interactive commands in a real pseudoterminal (node-pty in JavaScript, portable-pty in Rust)
• model terminal state with maintained emulators (@xterm/headless and vt100), with no custom VT parser
• drive text, control-key, and resize interactions
• retain consecutive-deduplicated settled frames and an ordered unrolled transcript
• preserve lines after they scroll outside the visible terminal
• record asciicast v2 output/input/resize events and provide readers in both languages
• write transcript, frame JSON, static SVG, and animated SVG artifacts
• retain and persist partial captures on timeout
• expose opt-in JavaScript tracing while keeping normal pipe/pipeline behavior unchanged
• provision a Node PTY host for Bun and use official node-pty prebuilds across Linux, macOS, and Windows

Verification

JavaScript:

• PATH=/tmp/formal-ai-841-bin:$PATH bun run test: 780 pass, 5 skip, 0 fail
• focused terminal suite repeated 10 times
• bun run lint
• bun run format:check
• bun run check:duplication
• CI: Bun on Ubuntu, macOS, and Windows; Node 20/22/24 on Ubuntu

Rust:

• red test first: unresolved command_stream::terminal
• focused terminal suite repeated 10 times
• cargo test --all-features
• cargo test --doc --all-features
• cargo clippy --all-targets --all-features
• cargo fmt --all -- --check
• cargo package --allow-dirty
• CI: Ubuntu, macOS, and Windows

Cross-language source parity also passes.