docs: api comments say what the endpoints do, not how they came to be (#6277)

Rewrites the internal/api comment blocks to rule 32: task, milestone and
rule ids gone, the stories behind them restated as the constraint they
left, stale references corrected (the stream secret is wired from config,
the timezone handler already refreshes the scheduler, the Android app is
the native client, the design docs cited are not in the repo). Also
rewraps comment lines over 80 columns left by the earlier batches.

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

internal/api/playlists.go

@@ -60,7 +60,7 @@ type playlistTrackView struct {
 	DurationSec int32   `json:"duration_sec"`
 	StreamURL   *string `json:"stream_url"`
 	AddedAt     string  `json:"added_at"`
-	// Unavailable marks an entry whose file is missing from disk (#2527).
+	// Unavailable marks an entry whose file is missing from disk.
 	// The track is still a real, known track — its history and likes are
 	// intact and the file may come back — so the entry keeps its place and
 	// its text; clients render it greyed out and skip over it on playback.
@@ -316,8 +316,9 @@ func (h *handlers) handleAppendTracks(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, playlistDetailToView(detail))
 }
 
-// handleRemovePlaylistTrack implements DELETE /api/playlists/{id}/tracks/{position}.
-// Owner only. Returns the post-mutation detail like AppendTracks.
+// handleRemovePlaylistTrack implements DELETE
+// /api/playlists/{id}/tracks/{position}. Owner only. Returns the post-mutation
+// detail like AppendTracks.
 func (h *handlers) handleRemovePlaylistTrack(w http.ResponseWriter, r *http.Request) {
 	caller, ok := requireUser(w, r)
 	if !ok {