chore: bootstrap pnpm workspace and package manifests

E00-S01-T01: create workspace/package manifests
- root package.json pins packageManager pnpm@11.23.0
- pnpm-workspace.yaml separates apps/*, packages/*, extensions/* entries
- skeleton manifests for apps/server, packages/core, extensions/example
- committed frozen lockfile generated by pnpm 11.23.0
- minimal CI: pnpm install --frozen-lockfile + workspace verification

.gitea/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  frozen-install:
+    name: Frozen lockfile install
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Node.js 24
+        uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+      - name: Enable pnpm (corepack, pinned to 11.23.0 via packageManager)
+        run: corepack enable
+      - name: Install dependencies (frozen lockfile)
+        run: pnpm install --frozen-lockfile
+      - name: Verify workspace groups
+        run: pnpm -r list --depth -1