add --no-agents flag to disable background agents

Disables memory scoring, surface, and observe agents when set.
Useful for testing with external backends (e.g. OpenRouter) where
background agent traffic would be slow and unnecessary.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/config.rs

@@ -445,6 +445,8 @@ pub struct SessionConfig {
     pub memory_file_count: usize,
     pub session_dir: PathBuf,
     pub app: AppConfig,
+    /// Disable background agents (surface, observe, scoring)
+    pub no_agents: bool,
 }
 
 /// A fully resolved model ready to construct an ApiClient.
@@ -514,6 +516,7 @@ impl AppConfig {
             config_file_count, memory_file_count,
             session_dir,
             app: self.clone(),
+            no_agents: cli.no_agents,
         })
     }