Fresh worktrees miss hugo-apps/node_modules — Hugo build fails until cd hugo-apps && npm install #214

Symptom

`npm run build:all` fails on a fresh git worktree because `hugo-apps/node_modules` doesn't exist. Root `npm install` populates the top-level dependencies, but `hugo-apps/` is its own npm project that needs its own `npm install` step.

Reproducer

```bash
git worktree add .worktrees/whatever -b some-branch
cd .worktrees/whatever
npm install # populates root node_modules
npm run fetch-tutorials # works
npm run build:all # FAILS — Hugo can't resolve @UI5 / vite-plugin-css-injected-by-js / etc.
```

The `hugo-apps/` build step inside `build:all` (Vite bundle for the Vue islands) needs its own dependency tree.

Why it matters

Multiple recurring failures during agent-driven implementation work (PR #197 navigator URL sync, PR #206 `/browse/` refactor) hit this. The recovery is always `cd hugo-apps && npm install` then retry, but it's invisible to the agent until the build fails. Memory pointer in CLAUDE plugin: `feedback-worktree-tests-hang` documents the symptom; this issue is for the underlying fix.

Proposed fixes (pick one or stack)

Option A — root postinstall

Add to root `package.json`:

```json
"scripts": {
"postinstall": "cd hugo-apps && npm install"
}
```

Runs automatically after every root `npm install`. Slight cost: every fresh `npm install` now takes longer. May want to gate on `hugo-apps/node_modules` absence to make it idempotent-cheap.

Option B — merge hugo-apps into the root workspace

Convert root `package.json` to use npm workspaces, with `hugo-apps` as one of the workspace members. Single `npm install` at the root resolves both dependency trees.

Risk: hugo-apps' `vite.config.ts` paths and the root scripts (`build:all`, etc.) might need adjustments. Larger change but the more correct long-term answer.

Option C — document in CLAUDE.md and the contributor guide

Add a note that fresh worktrees need `cd hugo-apps && npm install` after the root install. Minimum-cost solution but doesn't actually fix anything; just makes the workaround discoverable.

My recommendation

A for now (one-line script change, low risk, fixes the recurring agent friction). Revisit B if the workspaces refactor has other benefits.

Acceptance

• A fresh worktree's `npm install && npm run build:all` succeeds without the manual `cd hugo-apps && npm install` step.
• No regression to existing CI build (which works because CI runs both installs explicitly in the workflow YAML).

Out of scope

• Restructuring the hugo-apps source tree.
• Migrating away from Vite.