Agent Hotline v1.0.1

feat: build a downloadable Windows desktop installer

Package the app as a native installer alongside the npm CLI. The backend
is bundled into a self-contained executable (Node SEA via esbuild +
postject) and shipped as the Tauri sidecar, so the installed app needs no
Node runtime. In release builds the desktop shell spawns that sidecar and
points it at a per-user data dir; debug builds still run the backend source
with system Node.

Bundling lives in a separate installer config so the normal check pipeline
(which compiles without the sidecar binary) keeps passing. A manual
Desktop Release workflow builds the NSIS installer and uploads it to a
GitHub Release. The backend now honors AGENT_HOTLINE_DATA_DIR.