Remove sequence diagram from README

Removed mermaid sequence diagram illustrating the interaction between AI Agent and SentinelGate.

Author: Sentinel-Gate

README.md

@@ -31,18 +31,6 @@ SentinelGate sits between the AI agent and your system. Every action is intercep
   <img src="assets/diagram-how-it-works-2.svg" width="720" alt="How SentinelGate works">
 </p>
 
-```mermaid
-sequenceDiagram
-    participant Agent as AI Agent
-    participant SG as SentinelGate
-    participant Upstream as System / MCP Server
-
-    Agent->>SG: tools/call "delete_file"
-    Note over SG: Validate · Rate limit · Auth
-    Note over SG: Policy: "block-deletes" → DENY
-    SG-->>Agent: Access denied by policy
-    Note over Upstream: Never reached
-```
 
 No code changes. No agent modifications. Single binary, zero dependencies, sub-millisecond overhead.