refactor: the account pane becomes Fields, the pane for anything but a secret

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/app/layout.go

@@ -166,7 +166,7 @@ func (m *Model) layout() {
 	m.containers.SetSize(leftW, h[1])
 	m.secrets.SetSize(leftW, h[2])
 	m.detail.SetSize(m.w-leftW, avail)
-	m.srcDetail.SetSize(m.w-leftW, avail)
+	m.fields.SetSize(m.w-leftW, avail)
 }
 
 // active reports whether p is drawn focused: it has focus and the terminal
@@ -181,8 +181,8 @@ func (m Model) panesView() string {
 		func() string { return m.containers.View(m.st, m.active(paneContainers), spin) },
 		func() string { return m.secrets.View(m.st, m.active(paneSecrets), spin) },
 		func() string {
-			if m.srcDetail.Shown() {
-				return m.srcDetail.View(m.st, m.active(paneDetail), spin)
+			if m.fields.Shown() {
+				return m.fields.View(m.st, m.active(paneDetail), spin)
 			}
 			return m.detail.View(m.st, m.active(paneDetail), spin)
 		},