Follow the GDScript style guide in every script

- Types on every parameter, return value and variable, and snake_case names
  (the player name limit is the constant MAX_NAME_LENGTH).
- Spelling fixes: *_triggered, character_selected, separator, caught_errors.
  The server's catched_errors key stays as the server sends it.
- Signals are connected with signal.connect() instead of by name.
- Code is ordered signals, constants, exported vars, vars, @onready vars,
  functions, with @onready on one line and two blank lines between functions.
- Every script starts with a ## description. Template comments, old LOC notes
  and commented-out code are gone, apart from the local play code.
- Lines are at most 100 characters, apart from the local play path.
- The screenshot tour turns off the blinking text cursor so pictures match.

tests/unit/test_search.gd

@@ -1,4 +1,5 @@
 extends GdUnitTestSuite
+## How the search popup finds and orders matching soundtracks.
 
 const SearchWindowScript: GDScript = preload("res://search_popup.gd")
 
@@ -36,7 +37,8 @@ func test_ignores_spaces() -> void:
 
 
 func test_and_matches_ampersand() -> void:
-	assert_array(_search.find_matches("mario and luigi")).contains(["Mario & Luigi: Superstar Saga"])
+	assert_array(_search.find_matches("mario and luigi")) \
+			.contains(["Mario & Luigi: Superstar Saga"])
 
 
 func test_accented_letters_match_plain_letters() -> void: