feat: Settings is one page per section down a left rail, Account first, every setting a row; the profile form no longer saves blanks over your name and email (M503 #5595 #5596 #5597)

- /settings lands on Account: the Android app, profile, password, signed-in
  devices. Then Playback, Appearance, Notifications, Connections, About.
- Each setting is a row (name, one short line, control at the end) in a
  capped-width column; one-of-N choices are a shared Segmented control.
- Collection and Settings share one SectionRail.
- Connections leads ListenBrainz with a status line: not connected,
  connected and not sending, or sending with the last scrobble's age.
- Notifications prints its column labels once; the digest email's
  settings link points at /settings/notifications.
- #5596: the profile form now loads what is stored and sends only the
  fields that changed. It used to start blank, and the server reads a
  blank as "clear", so one Save wiped the display name and email.
- Recommendation metrics moves to Library › Your listening, and Hidden
  tracks gets a Library tab.

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

internal/notifications/digest_render.go

@@ -48,7 +48,7 @@ type digestVars struct {
 // renderDigest renders one group's email. base is the public address; with
 // none set, the email still goes out, without links.
 func renderDigest(group EmailGroup, name string, items []pendingItem, base string) (digestEmail, error) {
-	vars := digestVars{Name: name, SettingsURL: joinURL(base, "/settings#notifications")}
+	vars := digestVars{Name: name, SettingsURL: joinURL(base, "/settings/notifications")}
 	var subject string
 	if group == EmailSummary {
 		vars.Artists = summaryArtists(items, base)

internal/notifications/digest_test.go

@@ -154,7 +154,7 @@ func TestRenderDigest_SummaryGroupsByArtist(t *testing.T) {
 	require.Contains(t, e.Text, "  - Pure\n    https://music.example/albums/al-3")
 	require.Contains(t, e.Text, "Boards of Canada\n  https://music.example/artists/ar-2")
 	require.Contains(t, e.Text, "Tycho\n  - Awake")
-	require.Contains(t, e.Text, "https://music.example/settings#notifications")
+	require.Contains(t, e.Text, "https://music.example/settings/notifications")
 	require.Contains(t, e.HTML, `<a href="https://music.example/albums/al-1"`)
 }