build: migrate frontend tooling to pnpm + pin vite 8.0.3 (#666)

* build: migrate frontend tooling from yarn to pnpm

The Dockerfiles ran `yarn && yarn build`, which broke on node:24 (yarn no
longer on PATH; the corepack yarn shim made `npm i -g yarn` fail EEXIST),
while CI + Makefile used npm and only a yarn.lock was committed — an
inconsistent yarn/npm split. Standardize on pnpm, pinned via the
packageManager field + corepack.

- package.json: packageManager pnpm@11.6.0.
- pnpm-workspace.yaml: nodeLinker: hoisted (flat node_modules, npm/yarn-like, so
  directly-imported transitive deps like flatpickr resolve) + allow vue-demi's
  postinstall (it selects the Vue 3 entry). pnpm 11 reads these here, not .npmrc.
- Generate pnpm-lock.yaml (imported from yarn.lock); delete yarn.lock.
- Dockerfiles (dev/nginx/production): node:24 + `corepack enable && pnpm install --frozen-lockfile && pnpm build`.
- CI (check.yaml, docker.yaml): pnpm/action-setup + setup-node cache:pnpm; pnpm install --frozen-lockfile / pnpm build.
- Makefile, composer.json dev script, CLAUDE.md: npm/yarn -> pnpm.

pnpm build verified on a clean install (1425 modules, hoisted node_modules).

* fix(build): pin vite to 8.0.3 to fix rolldown chunk regression

vite 8.0.16 (pulled in by #653) bundles rolldown 1.0.3, which emits a
lazy chunk referencing an undefined Vue runtime-init function
(init_runtime_dom_esm_bundler), breaking the SPA at runtime. The build
succeeds so CI never caught it. Pin vite to 8.0.3 (the version 2.3.3
shipped, rolldown 1.0.0) which produces a correct bundle.

.github/workflows/docker.yaml

@@ -61,16 +61,20 @@ jobs:
       - name: Install Composer dependencies
         uses: ramsey/composer-install@v2
 
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+
       - name: Use Node.js 24
         uses: actions/setup-node@v4
         with:
           node-version: 24
+          cache: pnpm
 
       - name: Install
-        run: npm install
+        run: pnpm install --frozen-lockfile
 
       - name: Compile Front-end
-        run: npm run build
+        run: pnpm build
 
       - name: Apply tests ${{ matrix.php-version }}
         run: php artisan test
@@ -100,16 +104,20 @@ jobs:
         with:
           composer-options: --no-dev
 
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+
       - name: Use Node.js 24
         uses: actions/setup-node@v4
         with:
           node-version: 24
+          cache: pnpm
 
       - name: Install
-        run: npm install
+        run: pnpm install --frozen-lockfile
 
       - name: Compile Front-end
-        run: npm run build
+        run: pnpm build
 
       - name: Build Dist
         run: |