integration: add chat/README.md

chat/README.md

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+# DeepSeek V4 Chat — Sovereign Conversational Core
+
+> Model: **sovereign/deepseek-v4-sovereign** (304B MoE, sovereign-tuned,
+> MIT lineage — see `models/deepseek-v4-sovereign/`)
+
+## Quick start
+
+```bash
+# Local echo mode (no key needed)
+python3 -c "
+from chat.core import ChatSession, DeepSeekV4Client
+s = ChatSession(); s.add('user', 'hello')
+print(DeepSeekV4Client().complete(s)['content'][:80])
+"
+
+# API mode — set the key, then run the server
+export DEEPSEEK_API_KEY=hf_or_ds_...     # DeepSeek-compatible key
+export DEEPSEEK_API_BASE=https://api.deepseek.com/v1
+export DEEPSEEK_MODEL=sovereign/deepseek-v4-sovereign
+uvicorn chat.api.app:app --host 0.0.0.0 --port 8003
+# → POST /api/v1/chat/sessions · /send · GET /models · /status
+```
+
+The router is also wired into `src/sovereign/main.py` (guarded) — the full
+stack serves `/api/v1/chat/*`. Web UI: `site/chat.html`.
+
+## Env config
+
+| Env | Default | Purpose |
+|---|---|---|
+| `DEEPSEEK_API_BASE` | `https://api.deepseek.com/v1` | OpenAI-compatible base URL |
+| `DEEPSEEK_API_KEY` | *(unset)* | API key — unset ⇒ local echo mode |
+| `DEEPSEEK_MODEL` | `sovereign/deepseek-v4-sovereign` | Model id |
+
+## API
+
+| Method | Path | Purpose |
+|---|---|---|
+| POST | `/api/v1/chat/sessions` | Create a session |
+| GET | `/api/v1/chat/sessions/{id}` | Session + history |
+| POST | `/api/v1/chat/send` | Send message → reply (`{message, session_id, temperature?, max_tokens?}`) |
+| GET | `/api/v1/chat/models` | Model registry |
+| GET | `/api/v1/chat/status` | Mode / model / session count |
+
+## Tests
+
+```bash
+.venv/bin/pytest tests/test_chat.py -q    # 7 tests
+```
+
+## Honesty notes
+
+- Local echo mode is deterministic and offline — a smoke test, not a model.
+- The sovereign model card (304B MoE, GPTQ 4-bit) documents the
+  architecture; serving it at full scale requires the DeepSeek API or a
+  compatible runtime.