Add admin panel, WebSocket support, and API versioning

Introduce an admin portal (React + Nginx), WebSocket routing, and
API versioning middleware with `/api/v1/` prefix deprecation.
Add master API key authentication, new Prometheus metrics for AI
token consumption and active WebSockets, and extend S3 config
with a public endpoint URL. Update test paths and fixtures to
align with the new routing structure.

docs/SDK.md

@@ -0,0 +1,59 @@
+# Imago SDK - `imago-client`
+
+The official Python SDK provides an asynchronous, strongly-typed interface to the Imago API.
+
+## Installation
+
+```bash
+cd sdk
+pip install -e .
+```
+
+## Basic Usage
+
+The SDK provides an asynchronous Context Manager (`HubClient`) which handles connection pooling, retries, and authentication.
+
+```python
+import asyncio
+from imago_client import HubClient
+
+async def main():
+    async with HubClient("http://localhost:8000/api/v1", api_key="sk-test-secret-key") as client:
+        # 1. Upload an image
+        image = await client.images.upload("photo.jpg")
+        print(f"Uploaded! UUID: {image.uuid}")
+
+        # 2. Get status
+        details = await client.images.get(image.uuid)
+        print(f"Status: {details.processing_status}")
+        
+        # 3. Use AI
+        summary = await client.ai.draft_task("https://example.com/article", "Summarize this quickly.")
+        print(summary)
+
+if __name__ == "__main__":
+    asyncio.run(main())
+```
+
+## Advanced Features
+
+### 1. Resilient Retries
+By default, the SDK automatically retries requests on timeouts, TCP connection errors, `429 Too Many Requests`, and `5xx Server Errors`. It uses exponential backoff with jitter to ensure safe recovery.
+
+### 2. Real-Time Pipeline Streaming
+The SDK natively wraps the WebSockets API. You can `async for` over events until the pipeline finishes:
+
+```python
+async with HubClient(url, api_key) as client:
+    async for event in client.images.stream_pipeline_events("IMAGE_UUID"):
+        print(event["event"])
+        if event["event"] == "pipeline.done":
+            break
+```
+
+### 3. Error Handling
+All specific cases throw custom exceptions inherited from `ImagoError`:
+- `AuthError` (401)
+- `QuotaError` (403 or 429 quota exhaustion)
+- `NotFoundError` (404)
+- `PipelineError` (WebSockets specific)