add CI, .env.example, fix package name

- GitHub Actions CI: backend lint + import check, frontend typecheck + build
- .env.example with supported providers and model override
- Rename frontend package to codeabc-frontend v0.1.0
- Add repo topics: ai, code-reader, education, non-programmer, etc.

Author: he-yufeng

.env.example

@@ -0,0 +1,11 @@
+# LLM API Key — pick one provider
+OPENAI_API_KEY=sk-xxx
+# ANTHROPIC_API_KEY=sk-ant-xxx
+# DEEPSEEK_API_KEY=xxx
+
+# Model override (default: gpt-4o-mini)
+# CODEABC_MODEL=deepseek/deepseek-chat
+# CODEABC_MODEL=claude-sonnet-4-20250514
+
+# Frontend origin for CORS (default: http://localhost:5173)
+# FRONTEND_ORIGIN=https://your-domain.com

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  backend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - run: pip install -e ".[dev]"
+      - run: ruff check backend/
+      - run: python -c "from backend.app import app; print('Import OK')"
+
+  frontend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+      - run: cd frontend && npm ci
+      - run: cd frontend && npx tsc --noEmit
+      - run: cd frontend && npm run build

frontend/package.json

@@ -1,7 +1,7 @@
 {
-  "name": "frontend",
+  "name": "codeabc-frontend",
   "private": true,
-  "version": "0.0.0",
+  "version": "0.1.0",
   "type": "module",
   "scripts": {
     "dev": "vite",