[ChinaYiqun]

What changed

• adds a React 19 + TypeScript three-panel playground for knowledge-base documents, grounded chat, and retrieval evidence;
• adds a framework-free NanoHTTPD API with health, upload, text ingestion, document listing/deletion, and chat endpoints;
• returns answer and Top-K evidence together, including source document, chunk ID, similarity score, and original passage;
• adds a deterministic in-memory retrieval engine and offline tests, requiring no API key or database;
• supports optional Ollama generation while keeping the evidence contract unchanged;
• adds Docker Compose startup for the Java backend, Nginx-served React frontend, and optional Ollama profile;
• adds frontend and Compose validation to CI;
• adds bilingual README positioning and a complete playground/API guide.

Why

The repository previously had useful backend components but no coherent user-facing application. The old chat controller accepted form data, had no managed knowledge-base state, and returned generated text without retrieval evidence. Visitors could not upload a document, ask grounded questions, or inspect why an answer was produced.

This PR creates the product surface needed for demos, tutorials, social sharing, and practical secondary development:

Knowledge base | Grounded chat | Retrieval evidence

Default experience

docker compose up --build

Then open http://localhost:3000.

The default mode uses local hashing embeddings and an explicitly labeled extractive generator, so it runs without credentials or a model download. For real local generation:

RAG_PLAYGROUND_MODE=ollama docker compose --profile ollama up --build

API

• GET /api/health
• GET /api/documents
• POST /api/documents
• POST /api/documents/text
• DELETE /api/documents/{id}
• POST /api/chat

Validation

GitHub Actions runs:

bash scripts/check-no-hardcoded-secrets.sh
mvn --batch-mode --no-transfer-progress test
bash scripts/run-no-api-demo.sh
cd frontend && npm install --no-audit --no-fund && npm run build
docker compose config --quiet

Current boundaries

• document state and vectors are in memory and reset with the backend;
• the default local embedding/generator path is for deterministic demos, not production semantic quality;
• authentication, quotas, async ingestion, persistent vector storage, and multi-tenant isolation remain future work.