v2.0.1: ACP dispatch + PTY fallback + worktree management

Phase 5 of v2.0. External agent dispatch via SSH to host.

ACP dispatch (acp-dispatch.ts): spawns agent via SSH with JSON-RPC
stdio pipe. Wraps opencode/goose in ACP mode. Captures structured
events (file operations, tool calls) mapped to parts taxonomy.
Falls back to PTY if ACP handshake fails.

PTY dispatch (pty-dispatch.ts): raw SSH spawn for agents without ACP
support (claude, pi). Captures stdout/stderr as plain text. Simpler
but less structured than ACP.

SSH helper (ssh.ts): shared spawn wrapper for SSH commands to
samkintop@100.114.205.53 (Tailscale IP, same as booterm). Uses
openssh-client installed in the runtime Dockerfile stage.

Worktree management (worktrees.ts): createWorktree (git worktree add
via SSH), diffWorktree (git diff HEAD...task-branch), cleanupWorktree
(git worktree remove --force). One worktree per task at
/tmp/booworktrees/<taskId>.

Dispatcher updated: checks available_agents.supports_acp to pick
transport. Path B flow: create worktree → dispatch agent → diff
worktree → queue diff into pending_changes → cleanup worktree →
mark task complete.

Agent probe updated: probes via SSH to find host-installed agents
(which opencode && opencode --version over SSH).

Dockerfile: openssh-client added to runtime stage.
Config: SSH_HOST env var (default 100.114.205.53).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/coder/package.json

@@ -12,6 +12,7 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "@agentclientprotocol/sdk": "^0.22.1",
     "@boocode/server": "workspace:*",
     "@fastify/static": "^7.0.4",
     "@fastify/websocket": "^10.0.1",