Improve wording in terminology cleanup

Replace the placeholder noun left by the previous pass with context-fit
phrasing (arrangement XML, chart, custom songs, etc.).

tests/js/highway_3d_fret_spacing.test.js

@@ -1,5 +1,5 @@
 // Pins the fret-spacing setting in plugins/highway_3d/screen.js (PR #329).
-// The board can render fret columns either Uniform (equal width, the source game
+// The board can render fret columns either Uniform (equal width, the chart
 // Remastered style) or Logarithmic (real instrument geometry), switchable at
 // runtime via window.h3dSetFretSpacing and persisted in localStorage. A
 // refactor that renames the storage key, drops the uniform/log branch in

tests/test_library_filters.py

@@ -294,7 +294,7 @@ def test_year_sort_asc_oldest_first(client, seeded):
 
 def test_tuning_sort_down_tuned_before_up_tuned_at_same_distance(client, server_mod):
     """Within an ABS(tuning_sort_key) tier, the down-tuned variant
-    must come before the up-tuned one so the order matches the source game's
+    must come before the up-tuned one so the order matches the chart's
     grouping (Eb Standard before F Standard at distance 6, etc.).
     Earlier code used signed-key DESC for the tiebreaker, which put
     +6 before -6 — the opposite of intent. Regression for Copilot

tests/test_song.py

@@ -133,7 +133,7 @@ def test_int_optional_falls_back_on_overflow():
 def test_parse_note_falls_back_to_default_on_malformed_numeric_attrs():
     """Malformed numeric XML attributes degrade gracefully.
 
-    Third-party the source game XML occasionally emits empty / non-numeric
+    Third-party arrangement XML occasionally emits empty / non-numeric
     values for fields like `rightHand`. `_int_optional` (used for
     optional metadata fields like `rightHand` and `pickDirection`)
     falls back to the caller's default instead of raising, so a