docs: plan-era "v1", "Task N" and "Phase N" wording restated as facts (#6277)

The marker list behind the earlier server and web passes did not catch
"for v1", "Task 5", "Phase 2" or "today: Flutter". Those comments now say
what the code does.

Corrected: coverart said "both v1 providers" ship on. There are four
providers (MBCAA, TheAudioDB, Deezer, Last.fm), and Last.fm, which needs a
key, ships off.

Non-comment tokens unchanged against HEAD: 10 Go files, 7 TS/Svelte files.

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

internal/subsonic/types.go

@@ -48,8 +48,8 @@ func parseUUID(s string) (pgtype.UUID, bool) {
 	return u, u.Valid
 }
 
-// MusicFolder matches Subsonic's /rest/getMusicFolders. v1 always reports a
-// single folder because Minstrel has no multi-library concept yet.
+// MusicFolder matches Subsonic's /rest/getMusicFolders. Minstrel always
+// reports a single folder: it has no multi-library concept.
 type MusicFolder struct {
 	XMLName xml.Name `json:"-" xml:"musicFolder"`
 	ID      int      `json:"id" xml:"id,attr"`