CI workflow

Adds .github/workflows/ci.yml that runs on push/PR to main, executing
Biome check, ESLint, typecheck, tests, and build steps with pnpm 10 on
Node 22.

.github/workflows/ci.yml

@@ -0,0 +1,40 @@
+# .github/workflows/ci.yml
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+
+      - name: Biome check
+        run: pnpm biome check packages/
+
+      - name: ESLint (Solid rules)
+        run: pnpm eslint packages --ext .ts,.tsx
+
+      - name: Type check
+        run: pnpm -r typecheck
+
+      - name: Tests
+        run: pnpm -r test
+
+      - name: Build
+        run: pnpm -r build