labs: AICharts demo Worker (NL -> validated chart spec, D1, workers.dev) (#35)

Library (aicharts.js): spec validator, fixed ops (filter/group/sort/bin/limit),
Chart.js config, attach() for existing charts, <ai-chart> element.
Worker: sample orders in D1, schema/sample/aggregates to Workers AI with
structured output + one repair round, saved_charts, per-IP and daily caps.
deploy.py: workers.dev only, no DNS. For teahub matcha/teahub#93.


Claude-Session: https://claude.ai/code/session_01VDkN7ukK1kXkqov8FaZxva

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/labs-aicharts.yml

@@ -0,0 +1,34 @@
+name: labs-aicharts
+# Deploy the AICharts demo Worker (workers.dev, one D1, Workers AI), then smoke-test it. Manual only.
+on: workflow_dispatch
+permissions:
+  contents: read
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          sparse-checkout: .github/time
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+      - run: node .github/time/labs/aicharts/test_aicharts.mjs
+      - id: deploy
+        run: |
+          python3 .github/time/labs/aicharts/deploy.py | tee out.json
+          echo "url=$(python3 -c 'import json; print(json.load(open("out.json"))["url"])')" >> "$GITHUB_OUTPUT"
+        env:
+          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          CLOUDFLARE_ACCOUNT_ID: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+      - name: smoke
+        run: |
+          u="${{ steps.deploy.outputs.url }}"
+          for i in 1 2 3 4 5 6; do curl -fsS "${u}api/health" && break; sleep 10; done
+          curl -fsS "${u}api/schema?dataset=orders" | python3 -c 'import json,sys; d=json.load(sys.stdin); assert len(d["sample"])==5, d; print("schema ok")'
+          curl -fsS -X POST "${u}api/spec" -H 'content-type: application/json' \
+            -d '{"dataset":"orders","prompt":"total revenue by region"}' | tee spec.json
+          echo
+          echo "### AICharts: ${u}" >> "$GITHUB_STEP_SUMMARY"
+          echo '```json' >> "$GITHUB_STEP_SUMMARY"; cat spec.json >> "$GITHUB_STEP_SUMMARY"; echo '```' >> "$GITHUB_STEP_SUMMARY"