chore: use Task, split workflows

.github/workflows/docs.yml

@@ -0,0 +1,20 @@
+name: Build Docs
+
+on:
+  pull_request:
+    paths:
+      - 'www'
+      - '*.md'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Install Task
+        uses: go-task/setup-task@v1
+      - name: Build site
+        run: task docs