Improve built-in terminal reliability and remote replay performance

[Diffuzmetall]

Closes #1075.

Summary

• batch raw PTY output into ordered chunks and preserve arbitrary UTF-8/binary bytes end to end
• add bounded browser and daemon websocket backpressure, bad-socket isolation, heartbeat/reconnect, input queuing, and sequence deduplication
• reconnect from the last received sequence and bound initial browser replay to the latest 512 KiB instead of replaying the full 4 MiB scrollback on every open
• serialize terminal restart, open the replacement before closing the old PTY, and wait for daemon exit acknowledgement so final output precedes exit
• keep threadless terminal caches current, make latest-attached clients own resize, and restore ownership on failed attach/detach
• enable xterm Unicode 11 width rules and Nerd Font fallbacks
• bump the host-daemon protocol from 75 to 76 for byte-preserving input and required bounded-replay fields

Measurements

Sustained output

A local 16 MiB output probe improved from about 6.5 MiB/s to 53–63 MiB/s. Websocket output messages dropped from 16,386 to 258–480 depending on PTY chunking.

Input remained responsive during a 16 MiB remote flood. Over the Tailscale path used for QA, the full burst completed without disconnect while a concurrent input echo returned in 101 ms.

Reopening a populated remote terminal

Measured through an SSH tunnel to a patched VPS:

	Before	After
Time to final replayed line	2,210 ms	556 ms
Replay bytes	4,192,407	461,853
Websocket output messages	1,025	15

A subsequent reconnect requested the previous nextSeq and replayed only 319 bytes rather than the retained history.

Input integrity

A 200,009-byte payload containing emoji and combining characters crossed multiple 64 KiB request boundaries on the VPS with an exact SHA-256 match. CLI --stdin also has coverage for invalid UTF-8 bytes.

Validation

On current main:

• pnpm exec turbo run typecheck for app, CLI, host daemon, host-daemon contract, server, SDK, server contract, and templates
• 191 focused tests across app terminal UI/transport/controller, CLI terminal commands, daemon connection/PTY manager, server hub/routes, and both contracts
• production builds for app, CLI, server, and host daemon
• patched local and VPS live stacks, including latency, flood/backpressure, atomic restart, large paste, replay truncation, reconnect, and multi-client resize ownership