feat: add AI provider commands with on-chain payment

- Create ai.py with serve and request commands
- request includes balance verification and payment via blockchain send
- serve runs FastAPI server and optionally registers jobs with coordinator
Update marketplace.py:
- Add gpu unregister command (DELETE endpoint)

cli/aitbc_cli/commands/marketplace.py

@@ -300,6 +300,34 @@ def pay(ctx, booking_id: str, amount: float, from_wallet: str, to_wallet: str, t
     except Exception as e:
         error(f"Payment failed: {e}")
 
+@gpu.command()
+@click.argument("gpu_id")
+@click.option("--force", is_flag=True, help="Force delete even if GPU is booked")
+@click.pass_context
+def unregister(ctx, gpu_id: str, force: bool):
+    """Unregister (delete) a GPU from marketplace"""
+    config = ctx.obj['config']
+    
+    try:
+        with httpx.Client() as client:
+            response = client.delete(
+                f"{config.coordinator_url}/v1/marketplace/gpu/{gpu_id}",
+                params={"force": force},
+                headers={"X-Api-Key": config.api_key or ""}
+            )
+            
+            if response.status_code == 200:
+                result = response.json()
+                success(f"GPU {gpu_id} unregistered")
+                output(result, ctx.obj['output_format'])
+            else:
+                error(f"Failed to unregister GPU: {response.status_code}")
+                if response.text:
+                    error(response.text)
+    except Exception as e:
+        error(f"Network error: {e}")
+
+
 @gpu.command()
 @click.argument("gpu_id")
 @click.pass_context