fix(lyrics): align usability checks with shared fixtures

Trim after removing inline timestamps before matching speaker prefixes in Dart. Run one 21-case usability corpus through Dart, Go, and Kotlin tests.

Document the shared fixture and trigger Dart and Go CI when its resources change.

android/app/src/test/kotlin/com/zarz/spotiflac/NativeFinalizationPolicyTest.kt

@@ -7,6 +7,29 @@ import org.junit.Assert.assertTrue
 import org.junit.Test
 
 class NativeFinalizationPolicyTest {
+    @Test
+    fun matchesSharedLyricUsabilityCases() {
+        val stream = checkNotNull(
+            javaClass.getResourceAsStream("/lyrics_usability_cases.tsv"),
+        )
+        stream.bufferedReader().useLines { lines ->
+            for (line in lines) {
+                if (line.isBlank() || line.startsWith("#")) continue
+                val fields = line.split('\t')
+                assertEquals("invalid shared fixture: $line", 3, fields.size)
+                val lyrics = fields[2]
+                    .replace("\\n", "\n")
+                    .replace("\\r", "\r")
+                    .replace("\\t", "\t")
+                assertEquals(
+                    fields[0],
+                    fields[1].toBooleanStrict(),
+                    NativeFinalizationPolicy.hasUsableLyricsContent(lyrics),
+                )
+            }
+        }
+    }
+
     @Test
     fun usableLyricsRejectsHeadersButKeepsRealAndInstrumentalContent() {
         assertFalse(

android/app/src/test/resources/lyrics_usability_cases.tsv

@@ -0,0 +1,23 @@
+# Shared Dart/Go/Kotlin lyric-usability cases.
+# Columns: name<TAB>expected boolean<TAB>lyrics. Decode literal \n, \r, \t in lyrics.
+empty	false	
+whitespace	false	 \t\r\n 
+metadata_only	false	[ar:Artist]\n[ti:Title]\n[offset:0]
+metadata_case	false	[AR:Artist]\n[BY:SpotiFLAC]
+instrumental	true	 [Instrumental:TRUE] 
+timestamps_only	false	[00:01.00]\n<00:01.10>
+multiple_timestamps	false	[00:01.00][01:02:500] 
+speaker_only	false	v1:\n V2: 
+inline_before_spaced_speaker	false	[00:00.00]<00:00.01> v1:
+inline_before_tabbed_speaker	false	[00:00.00]<00:00.01>\tV2:\t
+multiple_inline_speaker	false	[00:00.00]<00:00.01> <00:00.02> v2: 
+empty_background	false	[bg: ]
+empty_timed_background	false	[bg:[00:00.00]<00:00.01> v1: ]
+plain_text	true	First line\nSecond line
+timed_text	true	[00:01.00]First line
+timed_speaker_text	true	[00:02:500]<00:02.500> v2: Harmony line
+background_text	true	[bg:Backing vocal]
+timed_background_text	true	[BG:[00:00.00]<00:00.01> v1: Backing vocal]
+multiple_timed_text	true	[00:01.00][00:02.00]Repeated line
+metadata_and_text	true	[ti:Title]\n[00:00.00]Actual lyric
+unicode_text	true	[00:00.00]<00:00.01> v1: 日本語の歌詞