feat(remote): provision daemon-created worktrees like the desktop

[Zeus-Deus]

Closes #78

Summary

The headless daemon's worktree_create MCP tool now runs the same post-create pipeline as the desktop, so workspaces created on a remote host are provisioned (deps, .env, env vars, port) and start from the latest remote commit.

• Shared setup core: crate::scripts::run_setup_commands is a new UI-free extraction of the setup-command loop. The desktop's run_setup_scripts_with_config is now a thin wrapper that forwards SetupEvents as the unchanged Tauri events — one command loop for both paths, no duplication.
• Daemon provisioning (remote/tools/mod.rs::provision_worktree_workspace):
  • gitignored include files (.env & co, .codemuxinclude → defaults) are copied from the parent repo synchronously, before the tool returns
  • .codemux/config.json setup commands run on a detached background thread with CODEMUX_ROOT_PATH / CODEMUX_WORKSPACE_PATH / CODEMUX_BRANCH / CODEMUX_PORT (+ NAME/ID), using the same deterministic allocate_workspace_port as the desktop
  • the tool response gains a setup summary: {port, includes_copied, setup_commands, setup_running}
  • progress/failures log to the daemon's stderr (journal); a failing setup script never fails the tool call
• Fetch-before-branch already landed in remote/git.rs ([git] Fetch origin before creating a new workspace branch so it starts from the latest remote #76 parity); this PR covers it end-to-end through the daemon.
• Test hygiene: the serve-test fixture now isolates HOME, so the integration suite stops rewriting the developer's real agent configs (~/.claude.json, …) with paths to transient debug binaries. The commands::mcp discovery test is scoped to project-level sources so a legitimate user-level codemux entry no longer fails it.

Headless config is file-based only (.codemux/config.json in worktree → repo root) — the Settings-UI fallback lives in the desktop SQLite DB, which doesn't exist on a headless host.

Acceptance criteria

• Remote-created workspaces run the project's setup script (deps/.env provisioned)
• Remote-created new branches start from freshly-fetched origin/<base>
• CODEMUX_* env vars + a unique port are present for remote workspaces
• Graceful behavior with no setup script / offline host (tool succeeds, falls back to local refs)

Testing

• Unit (remote/tools/mod.rs): setup script runs with correct CODEMUX_* env + reported port, .env copied; no-config repo reports setup_commands: 0; failing setup script doesn't fail the tool.
• Integration (tests/codemux_remote_serve_mcp.rs::http_worktree_create_provisions_like_desktop): real daemon over HTTP with a stale-clone scenario — new branch lands on the freshly-fetched origin tip (not the stale local ref), includes copied, setup marker written with correct env.
• Live E2E: built codemux-remote and ran it in an Arch container as the remote host, driven over HTTP with curl — verified fresh-tip branching, .env copy, env marker, sequential multi-command setup, graceful no-config repo, and offline-origin fallback.
• npm run verify fully green (all cargo suites, typecheck, 1826 frontend tests).

Docs updated: docs/core/STATUS.md, docs/features/setup-teardown.md (§ Headless Daemon Parity), docs/features/worktree-setup.md, docs/features/remote-hosts.md, docs/plans/mcp-on-remote.md.