added chat client documentation

docs/services/orchestration-service.md

@@ -14,10 +14,11 @@ or inference services — all traffic flows through orchestration.
 
 ## Dependencies
 
-- `express` — HTTP API
-- `node-fetch` — inter-service HTTP communication (memory service client only)
-- `dotenv` — environment variable loading
-- `@nexusai/shared` — shared utilities
+- `express` : HTTP API
+- `cors` : cross-origin resource sharing middleware
+- `node-fetch` : inter-service HTTP communication (memory service client only)
+- `dotenv` : environment variable loading
+- `@nexusai/shared` : shared utilities
 
 > `memory.js` uses `node-fetch` v2 (pinned) because it is CommonJS. All other
 > service clients use Node.js built-in `fetch`.
@@ -31,6 +32,7 @@ or inference services — all traffic flows through orchestration.
 | EMBEDDING_SERVICE_URL | No | http://localhost:3003 | Embedding service URL |
 | INFERENCE_SERVICE_URL | No | http://localhost:3001 | Inference service URL |
 | QDRANT_URL | No | http://localhost:6333 | Qdrant URL for semantic search |
+| CORS_ORIGIN | No | http://localhost:5173 | Allowed origin for CORS requests |
 
 ## Internal Structure
 ```
@@ -138,6 +140,7 @@ the `{"done":true}` event.
 
 | Method | Path | Description |
 |---|---|---|
+| GET | /sessions | Get paginated list of all sessions |
 | GET | /sessions/:sessionId/history | Get paginated episode history for a session |
 
 ---
@@ -215,4 +218,30 @@ Response:
 }
 ```
 
+---
+
+**GET /sessions**
+
+Returns a paginated list of all sessions, ordered by most recently active.
+
+Query parameters:
+
+| Parameter | Default | Description |
+|---|---|---|
+| limit | 20 | Maximum number of sessions to return |
+| offset | 0 | Number of sessions to skip (for pagination) |
+
+Response:
+```json
+[
+  {
+    "id": 1,
+    "external_id": "test-semantic",
+    "metadata": null,
+    "created_at": 1712345678,
+    "updated_at": 1712345999
+  }
+]
+```
+
 Episodes are ordered newest first. Returns `404` if the session does not exist.