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/api/me_profile.go

@@ -23,7 +23,7 @@ type updateProfileReq struct {
 	// nil = leave unchanged; non-nil empty string = clear; non-nil
 	// non-empty = update to that value. Note: distinguishing
 	// omit-vs-clear at JSON-decode time requires custom unmarshaling
-	// or a sentinel; for v1 we use the simpler "empty string clears"
+	// or a sentinel; we use the simpler "empty string clears"
 	// semantics: any field present in the JSON body is applied.
 	DisplayName *string `json:"display_name"`
 	Email       *string `json:"email"`