Adds `wsh attach` — a command that streams the live output of any Wave
Terminal block to a local terminal window without affecting the remote
session. Useful for monitoring long-running processes, CI jobs, or AI
coding agents from a separate window or SSH session.
Key capabilities:
- Interactive block selector (workspace → tab → block)
- Live PTY streaming via snapshot + WPS event subscription
- Viewport model: server PTY size is fixed; local terminal is a
moveable window into the remote screen (Ctrl+Arrow to pan)
- Diff-based renderer that emits only changed cells per frame,
with full SGR, wide-character, alt-screen, and cursor-style sync
- Debounced render loop (16 ms) coalesces rapid PTY bursts so that
full-screen TUI repaints are always consumed before rendering
- Resync command (Ctrl-A s) rebuilds xterm-go state from a fresh
snapshot when local state drifts from the remote
Bug fix included: EventRecv messages are now dispatched synchronously
in the WshRpc message loop (same pattern as StreamData/StreamDataAck)
so that back-to-back PTY events are always processed in arrival order.
Without this fix, concurrent goroutines race to write PTY chunks into
the terminal emulator, producing mixed-frame garbling.
