llm: fix duration timer — start before subprocess, not after

src/llm.rs

@@ -59,6 +59,8 @@ fn call_model(agent: &str, model: &str, prompt: &str) -> Result<String, String>
         cmd.env("CLAUDE_CONFIG_DIR", dir);
     }
 
+    let start = std::time::Instant::now();
+
     let result = unsafe {
         cmd.pre_exec(|| {
                 libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGTERM);
@@ -67,8 +69,6 @@ fn call_model(agent: &str, model: &str, prompt: &str) -> Result<String, String>
             .output()
     };
 
-    let start = std::time::Instant::now();
-
     fs::remove_file(&tmp).ok();
 
     match result {