## Summary
Add the G0 Godot Stage sidecar preview for `stage-tamagotchi`.
## Design
- Keep Electron as the desktop host and run Godot as a separate sidecar
window by design.
- Use the settings window as the entry point for starting/stopping the
experimental Godot Stage.
- Require explicit `GODOT4` in development mode instead of
auto-discovering local Godot installs.
- Use the packaged sidecar under `process.resourcesPath/godot-stage` in
the packaged runtime.
- Close the Godot WebSocket lifecycle channel on startup failure and
stage shutdown.
## Changes
- Add the Electron main-side Godot Stage lifecycle service.
- Add renderer/settings wiring for switching to the experimental Godot
Stage.
- Add the minimal Godot stage runtime skeleton and WebSocket handshake
path.
- Add Godot export presets for sidecar builds.
- Add sidecar path verification for the Godot export preset and
`electron-builder` resource contract.
- Document the development runtime setup and packaging expectations.
## CI/CD
- Align Godot CI to `4.6.2`.
- Add Linux Godot export smoke coverage as the fastest CI export path.
- Add sidecar contract verification to CI.
- Run packaged sidecar verification after `electron-builder --dir`.
CD is intentionally deferred in this PR. The release workflow still
needs a later step to export the Godot sidecar before packaging release
artefacts.
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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
