Add CLI startup time test to catch slow imports

Runs `cf --help` and fails if startup exceeds 200ms. Shows timing
info in CI logs on both pass and failure.

tests/test_cli_startup.py

@@ -0,0 +1,50 @@
+"""Test CLI startup performance."""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+import time
+
+# Threshold in seconds
+CLI_STARTUP_THRESHOLD = 0.2
+
+
+def test_cli_startup_time() -> None:
+    """Verify CLI startup time stays within acceptable bounds.
+
+    This test ensures we don't accidentally introduce slow imports
+    that degrade the user experience.
+    """
+    cf_path = shutil.which("cf")
+    assert cf_path is not None, "cf command not found in PATH"
+
+    # Run multiple times and take the minimum to reduce noise
+    times: list[float] = []
+    for _ in range(3):
+        start = time.perf_counter()
+        result = subprocess.run(
+            [cf_path, "--help"],
+            check=False,
+            capture_output=True,
+            text=True,
+        )
+        elapsed = time.perf_counter() - start
+        times.append(elapsed)
+
+        # Verify the command succeeded
+        assert result.returncode == 0, f"CLI failed: {result.stderr}"
+
+    best_time = min(times)
+    avg_time = sum(times) / len(times)
+
+    # Always print timing info - visible in CI logs even on failure
+    msg = (
+        f"\nCLI startup times: {[f'{t:.3f}s' for t in times]}\n"
+        f"Best: {best_time:.3f}s, Avg: {avg_time:.3f}s, Threshold: {CLI_STARTUP_THRESHOLD}s"
+    )
+    print(msg)
+
+    assert best_time < CLI_STARTUP_THRESHOLD, (
+        f"CLI startup too slow!\n{msg}\nCheck for slow imports."
+    )