…phase

The `bundle_ui` step previously carried a `generatesAssetsManifest: boolean` config that fired for every command (`build`, `dev`, `deploy`) because the framework hardcoded a single `'deploy'` lifecycle. The flag is the smell: bundle_ui was doing two jobs and conditionally turning the second one off.

This change splits the manifest emission into its own step (`generate_ui_assets_manifest`) and replaces the single `'deploy'` lifecycle with two additive phases:

- `'build'` — local build (run by `shopify app build`).
- `'bundle'` — extra steps run after `'build'` when bundling for upload (driven by `dev` and `deploy`). Specs only declare a `'bundle'` group when they need to do more than the local build.

`extension.build()` composes them: `'build'` runs only the build steps; `'bundle'` runs `[...buildSteps, ...bundleSteps]` in declaration order. No spec needs to duplicate steps across both groups.

For `ui_extension`: `'build'` runs `bundle_ui`; `'bundle'` adds `generate_ui_assets_manifest` and `include_assets`. Net result: `shopify app build` no longer emits `manifest.json` for `ui_extension`; `dev` and `deploy` are unchanged.

The other 13 specs simply rename `lifecycle: 'deploy'` → `lifecycle: 'build'` — same behavior as before across all three commands.

`include_assets` keeps its own `generatesAssetsManifest` flag (out of scope for this PR; same cleanup pattern can be applied later).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>