Add docs for API & the agent architecture (#22)

* Add docs for API & the agent
* Add reAct arch diagram

docs/api/index.md

@@ -0,0 +1,106 @@
+# API Reference
+
+The Geo Assistant API provides a streaming chat endpoint for geographic queries.
+
+## Base URL
+
+```
+http://localhost:8000
+```
+
+## Endpoint
+
+### POST /chat
+
+Stream chat responses from the geographic assistant agent.
+
+**Request Body**
+
+```json
+{
+  "thread_id": "uuid-string",
+  "agent_state_input": {
+    "messages": [
+      {
+        "type": "human",
+        "content": "Your question here"
+      }
+    ]
+  }
+}
+```
+
+**Schema**
+
+- `thread_id` (string): UUID for conversation thread
+- `agent_state_input` (object):
+  - `messages` (array): Array of message objects with `type` and `content`
+
+**Response**
+
+Streaming NDJSON format (`application/x-ndjson`). Each line contains:
+
+```json
+{
+  "thread_id": "uuid-string",
+  "state": {
+    "messages": [...],
+    "place": {...},
+    "search_area": {...},
+    "naip_img_bytes": {...}
+  }
+}
+```
+
+**Example**
+
+```bash
+curl -X POST http://localhost:8000/chat \
+  -H "Content-Type: application/json" \
+  -d '{
+    "thread_id": "123e4567-e89b-12d3-a456-426614174000",
+    "agent_state_input": {
+      "messages": [{"type": "human", "content": "Your question"}]
+    }
+  }'
+```
+
+**Python Example**
+
+```python
+import json
+import uuid
+import httpx
+
+thread_id = str(uuid.uuid4())
+
+request_body = {
+    "thread_id": thread_id,
+    "agent_state_input": {
+        "messages": [{"type": "human", "content": "Your question"}]
+    },
+}
+
+with httpx.stream(
+    "POST",
+    "http://localhost:8000/chat",
+    json=request_body,
+    timeout=360.0,
+) as response:
+    response.raise_for_status()
+    
+    for line in response.iter_lines():
+        if not line:
+            continue
+        
+        data = json.loads(line)
+        state = data.get("state", {})
+        messages = state.get("messages", [])
+        
+        # Process messages
+        for msg in messages:
+            print(f"{msg['type']}: {msg['content']}")
+
+        # Process state updates
+        # ...
+```