feat(code): wire gRPC server into Sol startup

spawns gRPC server alongside Matrix sync loop when [grpc] config
is present. shares ToolRegistry, Store, MistralClient, and Matrix
client with the gRPC CodeSession handler.

src/brain/responder.rs

@@ -65,6 +65,11 @@ impl Responder {
         }
     }
 
+    /// Get a reference to the tool registry (for sharing with gRPC server).
+    pub fn tools(&self) -> Arc<ToolRegistry> {
+        self.tools.clone()
+    }
+
     pub async fn generate_response(
         &self,
         context: &[ContextMessage],

src/main.rs

@@ -293,6 +293,22 @@ async fn main() -> anyhow::Result<()> {
         error!("Reaction backfill failed (non-fatal): {e}");
     }
 
+    // Start gRPC server if configured
+    if config.grpc.is_some() {
+        let grpc_state = std::sync::Arc::new(grpc::GrpcState {
+            config: config.clone(),
+            tools: state.responder.tools(),
+            store: store.clone(),
+            mistral: state.mistral.clone(),
+            matrix: matrix_client.clone(),
+        });
+        tokio::spawn(async move {
+            if let Err(e) = grpc::start_server(grpc_state).await {
+                error!("gRPC server error: {e}");
+            }
+        });
+    }
+
     // Start sync loop in background
     let sync_client = matrix_client.clone();
     let sync_state = state.clone();