feat: add utility functions with tests

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

tests/test_utils.py

@@ -0,0 +1,22 @@
+import sys, os
+sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
+from main import build_export_path, format_time
+
+
+def test_build_export_path_first():
+    assert build_export_path("/out", "clip", 1) == "/out/clip_001.mp4"
+
+def test_build_export_path_counter():
+    assert build_export_path("/out", "clip", 42) == "/out/clip_042.mp4"
+
+def test_build_export_path_deep_counter():
+    assert build_export_path("/out", "shot", 999) == "/out/shot_999.mp4"
+
+def test_format_time_seconds():
+    assert format_time(0.0) == "0:00.0"
+
+def test_format_time_minutes():
+    assert format_time(75.3) == "1:15.3"
+
+def test_format_time_rounding():
+    assert format_time(61.05) == "1:01.0"