Distribution scaffold never installs @angular/compiler, so the host Explorer cannot build out of the box

Found on a bare `mj install -t v6.1.0-edge.6` (distribution layout) on 2026-09-12, immediately after working around the codegen-phase failure filed separately.

## What happens

`npm run build` at the host repo root fails at `mj_explorer#build` on a host nobody has touched:

```
✘ [ERROR] Angular compilation initialization failed. [plugin angular-compiler]
Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@angular/compiler' imported from
node_modules/@angular/compiler-cli/bundles/chunk-SOKUOCYN.js
```

## Cause

- `apps/MJExplorer/package.json` declares `"@angular/compiler-cli": "21.2.22"` and **does not declare `@angular/compiler` at all**, in `dependencies` or `devDependencies`.
- `@angular/compiler-cli`'s own manifest lists `"@angular/compiler": "21.2.22"` as a **peerDependency**, and imports it at runtime.
- `node_modules/@angular/` contains `compiler-cli` and **no `compiler`**. The host root `package.json` has no `overrides` that would explain it.

## Fix

Declare `@angular/compiler` at the platform pin in the scaffold's Explorer `devDependencies`, alongside the `compiler-cli` anchor already there. Verified: `npm install -w apps/MJExplorer @angular/compiler@21.2.22` clears this error.

This is the failure mode MJ's own guidance warns about for `ng-auth-services` — the Angular build cannot resolve a peer that is not installed, and it fails with a bare module-resolution error that names nothing useful — reaching the distribution scaffold itself.

## Environment

MJ `v6.1.0-edge.6`, distribution install, macOS, Node 24.20.0, npm.

Open apps/MJExplorer/package.json and compare the Angular compiler-related entries with the platform pin described in the issue. Run npm install -w apps/MJExplorer and then npm run build from the host repository root. Done means the distribution scaffold installs the required compiler package and mj_explorer#build no longer fails with the missing-module error.

Written by the indexing model from the issue text.