feat(desktop): native macOS app packaged as Apple Silicon DMG

[stretchcloud]

Summary

• Adds a native macOS desktop app (Apple Silicon) under desktop/, distributed as a DMG attached to GitHub Releases.
• The app is a thin Electron shell: it boots the full Campfire server (same Bun + Hono backend as npm/Docker) as a bundled sidecar — backend sources, a minimal production node_modules (hono, croner, @lancedb/lancedb), and the Bun runtime ship inside the .app — then loads the web UI in a native window. Every feature is included by construction.

Why

• One-click install for Mac users: no Bun, no terminal, no npm. Download DMG → drag to Applications.
• Distribution is free: ad-hoc signing (no Apple Developer account), DMG built on the free macos-14 runner, hosted on GitHub Releases.

Behavior

• Reuse-first: attaches to an existing Campfire on :4567 (service installs, bunx the-campfire) instead of double-spawning against ~/.campfire; otherwise spawns the sidecar on the first free port.
• Shared ~/.campfire state with the CLI/web flavors; sidecar logs at ~/.campfire/logs/desktop-server.log; Cmd+Q stops the sidecar, agent processes resume on next launch like any server restart.
• External links open in the default browser; native menu, window-state persistence, crash dialog with relaunch.

Notable fixes found along the way

• electron-builder silently drops node_modules from extraResources; the bundle appeared to work because Bun auto-installs missing packages at runtime (would break offline). The afterPack hook now copies them explicitly.
• codesign rejects node_modules/.bin symlinks — stripped during packaging.
• The orchestration MCP server was spawned via a bare bun PATH lookup; it now uses the running Bun executable's absolute path, so multi-agent tools work in the desktop app and on machines without a global Bun install.

Testing

• web: typecheck + full suite green (87 files, 1635 tests), including new coverage for the Bun-runtime MCP command branch.
• desktop: 6 unit tests for the boot helpers (free-port scan, Campfire probe, readiness wait).
• Manual: staged sidecar boots with the bundled Bun; Electron smoke run (spawn → load UI → clean exit); DMG mounted and launched; GUI (Finder) launch verified — cold start ~22 s (one-time Gatekeeper scan), warm ~3 s; clean teardown confirmed twice; signature verifies (codesign --verify --deep --strict).