fix(test): use PID-scoped script path to prevent ETXTBSY in CI

The echo_provider() test helper writes a fake_claude.sh script to
a shared temp directory. When lib and bin test binaries run in
parallel (separate processes, separate OnceLock statics), one
process can overwrite the script while the other is executing it,
causing "Text file busy" (ETXTBSY). Scope the filename with PID
to isolate each test process.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/providers/claude_code.rs

@@ -387,7 +387,7 @@ mod tests {
             use std::io::Write;
             let dir = std::env::temp_dir().join("zeroclaw_test_claude_code");
             std::fs::create_dir_all(&dir).unwrap();
-            let path = dir.join("fake_claude.sh");
+            let path = dir.join(format!("fake_claude_{}.sh", std::process::id()));
             let mut f = std::fs::File::create(&path).unwrap();
             writeln!(f, "#!/bin/sh\ncat /dev/stdin").unwrap();
             drop(f);