Fixes #184.

- Reuse the shared sidebar's + action for each locally available project in All Projects, with a project-specific accessible label and tooltip. - Create in the clicked project's checkout, select the new channel, and stay in All Projects. - Keep empty creatable projects visible and expand collapsed groups when creating. - Retain the existing connected/local-host restrictions and single-project behavior.

### Validation

- `bun types` - `bun run ci` - `bun run --filter @ace/app build` - Real Bun host and Safari/WebKit smoke test with isolated host/config directories and two temporary Git projects. Both empty projects showed +. With alpha current, beta's + created a channel under beta; then alpha's + expanded its collapsed heading and created under alpha. Both channels were selected while remaining in All Projects, and `ace info` confirmed their project paths. No models were invoked. - Independent review found no actionable issues.

### Built in Ace

Implemented, reviewed, built, and operated through Ace tools in a lane. Used Safari through Ace's native desktop tools for the lane UI smoke test because Browser Preview is not available in the current app (#16). No external editor or terminal. Installed native release verification remains separate.