feat(#30): Gate B [10/10]: Deploy compose + WOO_BASE_URL (OPS-1, GC-5)

- deploy/.env.example: placeholders only (no real URLs, proper comments)
- frontend/Dockerfile: Node 20 stub server for compose build
- deploy/tests/test-compose-health.sh: OPS-1 compose health smoke test
- deploy/tests/test-woo-base-url.sh: GC-4/5/FUND-25 validation suite
- backend/app/api/settings.py: PUT rejects woo_base_url (422), consumer keys (422),
  text() wrapping for SQLAlchemy 2.x, key primary key fix
- backend/tests/contract/test_woo_base_url.py: 8 contract tests for GC-4/GC-5

Tests: 39/39 backend tests pass (8 new, 31 existing green)
Deploy: 5/5 shell tests pass (Docker unavailable for compose-up path)

frontend/Dockerfile

@@ -0,0 +1,17 @@
+FROM node:20-slim
+
+WORKDIR /app
+
+COPY frontend/package*.json ./
+RUN npm ci --ignore-scripts
+
+COPY frontend/ .
+
+# Build the SvelteKit app (stub for Gate B — will be updated when SvelteKit scaffolds)
+# For now, copy a stub HTML page. Vite build runs in production mode later.
+RUN mkdir -p build && \
+    echo '<!DOCTYPE html><html><head><meta charset="utf-8"><title>SlabUploader</title></head><body><h1>SlabUploader — coming soon</h1><p>SvelteKit app stub. Update this Dockerfile when the SvelteKit app is scaffolded.</p></body></html>' > build/index.html
+
+EXPOSE 80
+
+CMD ["node", "-e", "const h=require('http'),fs=require('fs'),url=require('url');h.createServer((req,res)=>{const f='build/index.html';res.writeHead(200,{'Content-Type':'text/html'}).end(fs.readFileSync(f))}).listen(80);console.log('frontend on :80')"]