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/cast_token.go

@@ -20,7 +20,7 @@ const (
 type castTokenRequest struct {
 	TrackID    string `json:"trackId"`
 	ExpSeconds int    `json:"expSeconds,omitempty"`
-	// Level asks for the leveled stream (M464 #5001): the track rendered at
+	// Level asks for the leveled stream: the track rendered at
 	// the user's loudness gain. AsAlbum says the track is playing as part of
 	// its album in order, which picks album gain in auto mode; only the
 	// client holding the queue knows it.
@@ -68,7 +68,7 @@ func mimeForFormat(format string) string {
 // extension (Content-Type header alone is insufficient) -- without a
 // recognizable extension, Sonos reports TrackDuration=0 and seeks
 // trigger auto-advance because every position past 0 looks past-the-
-// end. Defaults to "mp3" for unknown formats. See task #610.
+// end. Defaults to "mp3" for unknown formats.
 func extForFormat(format string) string {
 	switch strings.ToLower(strings.TrimSpace(format)) {
 	case "mp3", "mpeg":
@@ -101,9 +101,6 @@ func extForFormat(format string) string {
 //
 // expSeconds is clamped to [60, 86400]; default 21600 (6h) — long enough
 // to play through any typical track without re-minting mid-playback.
-//
-// Part of the output-picker UPnP slice. See
-// docs/superpowers/specs/2026-06-03-android-output-picker-upnp-design.md.
 func (h *handlers) handleCastStreamToken(w http.ResponseWriter, r *http.Request) {
 	user, ok := requireUser(w, r)
 	if !ok {