build: migrate from npm to pnpm

Ten git worktrees each carried their own 225 MB node_modules (1.1 GB across
five) and paid 11s per `npm ci`. pnpm hardlinks from a shared store: the same
five worktrees cost ~250 MB total, and a fresh install is 4s.

What changed beyond the mechanical rename:

- `overrides` moved to `pnpm-workspace.yaml`. pnpm 11 does not read the `pnpm`
  field in package.json *or* npm's top-level `overrides`, and it fails silently
  — the vite/defu/language-server pins would have quietly stopped applying.
- Build scripts are blocked by default in pnpm; esbuild and sharp are allowed
  explicitly via `allowBuilds` (renamed from `onlyBuiltDependencies` in 11).
- `packageManager` + `engines` pin the toolchain.
- gate.sh rejects a package-lock.json/yarn.lock/bun.lock outright, so an agent
  running `npm install` out of habit fails loudly instead of building a second,
  divergent dependency tree.
- CI bootstraps pnpm with `npm install --global pnpm@11.25.0` rather than
  corepack (unbundled as of Node 25) or pnpm/action-setup (this self-hosted
  act-runner has never run a job; fetching a third-party action is not
  something to discover on the first one).

Two pre-existing CI bugs fixed while in the file:

- the gate installed with `npm install --package-lock=false`, which discarded
  the lockfile the previous session had just fixed.
- the visual-regression step imported `playwright`, which is not a dependency,
  and `visual-regression.mjs` has no compare mode anyway — in CI it overwrote
  its own baselines and passed unconditionally. Removed with a comment; it
  comes back when it can diff.

The `publish` job is now manual (`workflow_dispatch`). During the migration
dist/ holds three HTML files against the live pages branch's ten, so publishing
on every push to main would take the site down to a stub. Restore at task 20.

HANDOVER.md's incident log still says npm where it describes what happened at
the time; that is history, not a missed rename.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitea/workflows/verify.yml

@@ -6,6 +6,14 @@ on:
   push:
     branches: [main]
   pull_request:
+  # Publication is deliberately manual for the duration of the Astro migration.
+  # See the `publish` job below for why.
+  workflow_dispatch:
+    inputs:
+      publish:
+        description: 'Force-push dist/ to the pages branch'
+        type: boolean
+        default: false
 
 jobs:
   gate:
@@ -17,22 +25,27 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 22
-          cache: npm
-      - run: npm install --package-lock=false --prefer-offline
-      - run: npm run lint
+      # Node 25 dropped the bundled corepack, and this self-hosted act-runner
+      # is not a good place to discover whether it can fetch a third-party
+      # action. Bootstrapping pnpm with npm needs neither. Keep the version in
+      # step with package.json's `packageManager`.
+      - run: npm install --global pnpm@11.25.0
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm run lint
       - run: ./.agents/scripts/gate.sh
-      - name: visual regression
-        run: |
-          npx playwright install --with-deps chromium
-          node .agents/scripts/visual-regression.mjs
-      - uses: actions/upload-artifact@v4
-        if: failure()
-        with:
-          name: screenshots
-          path: .agents/snapshots/diff/
+      # The visual-regression step is intentionally absent. `visual-regression.mjs`
+      # only *captures* baselines — it has no compare mode — so in CI it would
+      # overwrite .agents/snapshots/before/ and pass unconditionally. It also
+      # imports `playwright`, which is not a dependency of this project. Wire it
+      # back in once it can actually diff. See task 03's report.
 
   publish:
-    if: github.ref == 'refs/heads/main'
+    # Until the migration finishes, `dist/` holds only /summary/ and the two
+    # hands-on fixtures, while the live `pages` branch serves ten pages.
+    # Publishing on every push to main would take the site down to a stub, so
+    # this job runs only when a human asks for it. Make it unconditional on
+    # main again at task 20 (cutover), not before.
+    if: github.event_name == 'workflow_dispatch' && inputs.publish
     needs: gate
     runs-on: ubuntu-latest
     steps:
@@ -40,9 +53,9 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 22
-          cache: npm
-      - run: npm install --package-lock=false --prefer-offline
-      - run: npm run build
+      - run: npm install --global pnpm@11.25.0
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm run build
       - name: Publish generated site to pages
         run: |
           git config user.name 'gitea-actions[bot]'