Conductor gstack template fails on new project creation with build exit code 128

## Summary
Creating a new project in Conductor with the `gstack` template fails after cloning the template with:

`Failed to create repo: error: script "build" exited with code 128`

## Repro
1. Open Conductor.
2. Choose the `gstack` template in Quick start.
3. Create a brand-new repo/project.
4. Conductor clones `.claude/skills/gstack` into the new project.
5. The install/build step fails with exit code `128`.

## What I verified
- GitHub auth can succeed and the template clone step completes.
- The failure happens after clone, during the template `build` script.
- `origin/main` currently contains this in `package.json`:

```json
"build": "... && git rev-parse HEAD > browse/dist/.version && git rev-parse HEAD > design/dist/.version && git rev-parse HEAD > make-pdf/dist/.version && ..."
```

## Likely root cause
In a freshly created repo before the first commit exists, `git rev-parse HEAD` exits with code `128`.

That makes the template fail in bootstrapping flows that run before the initial commit is created.

## Suggested fix
Use a fallback when `HEAD` does not exist yet, for example:

```json
(git rev-parse HEAD 2>/dev/null || echo unknown) > browse/dist/.version
(git rev-parse HEAD 2>/dev/null || echo unknown) > design/dist/.version
(git rev-parse HEAD 2>/dev/null || echo unknown) > make-pdf/dist/.version
```

This fixed the local reproduction when testing the template outside an initialized repo with commits.