docs: wanted, dbtest, recommendation and playlists comments say what the code does (#6277)

The same rewrite as d191a282, for four packages whose comments carried the
most history: tuning stories, quotes from the operator, single-install
measurements in library_scale.go, and 'used to' accounts of bugs. The
constraint each story protected stays as a present-tense reason (why tier 3
is reduced not removed, why the randomised arms take an order seed, why the
seed artist is eligible in Songs-like). Comments naming system_cron.go and
config.RecommendationConfig, neither of which holds what they claimed, now
name the scheduler and internal/recsettings.

Checked: non-comment tokens identical to HEAD; gofmt clean.

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

internal/wanted/search.go

@@ -18,8 +18,7 @@ import (
 	"git.fabledsword.com/bvandeusen/minstrel/internal/release"
 )
 
-// Searching for wants on a schedule (M502 #5521), ported from Fabled
-// Librarian's internal/wanted. The schedule decides which wants and when;
+// Searching for wants on a schedule. The schedule decides which wants and when;
 // internal/acquire judges what a search finds and grabs.
 
 // Search outcomes, matching wants_search_outcome_check.
@@ -32,7 +31,7 @@ const (
 
 const (
 	// searchTick is how often the schedule looks for wants due; the
-	// operator's setting is how long a want waits between searches.
+	// search interval setting is how long a want waits between searches.
 	searchTick = 10 * time.Minute
 	// searchWindow is how long one pass searches: most of a tick, so a pass
 	// ends before the next begins.
@@ -194,7 +193,7 @@ type searchRow struct {
 	artist, title, primary, date, group string
 	secondary                           []string
 	// upgrade, heldTier and held: a held album wanted for a better copy
-	// (#5524), and the copy it has.
+	// and the copy it has.
 	upgrade, heldTier, held string
 }
 
@@ -346,7 +345,7 @@ func (s *Searcher) Take(ctx context.Context, id pgtype.UUID, key string, force b
 }
 
 // load reads a want for a search: an open one, or a held album wanted for a
-// better copy (#5524).
+// better copy.
 func (s *Searcher) load(ctx context.Context, id pgtype.UUID) (acquire.Want, error) {
 	row, err := dbq.New(s.pool).GetWantForSearch(ctx, id)
 	if err != nil {