move pi-mono into companion-cloud as apps/companion-os

- Copy all pi-mono source into apps/companion-os/
- Update Dockerfile to COPY pre-built binary instead of downloading from GitHub Releases
- Update deploy-staging.yml to build pi from source (bun compile) before Docker build
- Add apps/companion-os/** to path triggers
- No more cross-repo dispatch needed

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/coding-agent/docs/windows.md

@@ -0,0 +1,17 @@
+# Windows Setup
+
+Pi requires a bash shell on Windows. Checked locations (in order):
+
+1. Custom path from `~/.pi/agent/settings.json`
+2. Git Bash (`C:\Program Files\Git\bin\bash.exe`)
+3. `bash.exe` on PATH (Cygwin, MSYS2, WSL)
+
+For most users, [Git for Windows](https://git-scm.com/download/win) is sufficient.
+
+## Custom Shell Path
+
+```json
+{
+  "shellPath": "C:\\cygwin64\\bin\\bash.exe"
+}
+```