docs: library comments say what the scanner and resolver do, not how they came to be (#6277)

Rewrites the internal/library comment blocks to rule 32. Task, milestone,
decision and rule ids are gone; the incidents behind them are restated as
the constraint they left (why a file is deleted before its row, why the
missing mark is a mark, why duplicates block on duration). Counts and
album names from one library are dropped from production comments; test
comments keep the names their fixtures use. The tagReadVersion log keeps
each version's before and after, without the measurements.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/id3v2genre.go

@@ -16,8 +16,8 @@ import (
 //
 // — it splits on the ID3v2 null separator and rejoins with the EMPTY string, so
 // a file tagged "Alternative Rock" + "Rock" comes back as the single token
-// "Alternative RockRock" (#2499). We stored that verbatim, which corrupted the
-// genre browse axis and polluted the taste profile's tag vocabulary.
+// "Alternative RockRock". Stored verbatim, that would corrupt the genre
+// browse axis and pollute the taste profile's tag vocabulary.
 //
 // ffprobe is not an escape hatch either: ffmpeg's read_ttag calls decode_str
 // exactly once with no loop, so it keeps only the FIRST value and silently