fix: say a sign-in error once, then in Details for that account (#4)

A failing account's error ("sign-in required … press L to run az login --tenant …") stayed in the footer for the whole session.

- **Footer:** it's now an ordinary message, shown once when an account's error first appears (at start, or when a load fails), and gone on the next key press. It's said again only when the errors change, or for another account.
- **Details:** with that account's group header or one of its sources selected, the Details pane shows the error and the sign-in hint, in place of "Select a vault or scope…".
- **`L`** signs in to the selected account when it needs it, else to the last one that asked, as before. With two accounts, `L` used to run whichever sign-in had failed most recently.

Test: two accounts, one failing to list its subscriptions. The message is in the footer at start and gone after a key press, in Details on that account's group, and `L` targets it. It isn't shown on the other account's rows.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #4

internal/ui/panes/detail.go

@@ -46,6 +46,7 @@ type Detail struct {
 
 	versions []provider.Object // newest first; nil while unknown
 	note     string            // the user's note on what's shown
+	message  string            // shown instead of the hint when nothing is selected: an error
 
 	offset int
 	w, h   int
@@ -71,6 +72,10 @@ func (d *Detail) Clear() {
 	*d = Detail{Now: d.Now, Icons: d.Icons, RevealKey: d.RevealKey, VersionsKey: d.VersionsKey, w: d.w, h: d.h} // drops the note too
 }
 
+// SetMessage sets what's shown instead of the hint when nothing is
+// selected, such as why an account has nothing to show; "" for the hint.
+func (d *Detail) SetMessage(s string) { d.message = s }
+
 // SetDescribing marks extra metadata as being fetched.
 func (d *Detail) SetDescribing() { d.describing, d.describeErr = true, nil }
 
@@ -186,6 +191,12 @@ func (d Detail) lines(st styles.Styles) []string {
 	muted := st.Muted.Render
 
 	if d.container == nil {
+		if d.message != "" {
+			for _, l := range strings.Split(ansi.Hardwrap(d.message, max(1, inner-2), true), "\n") {
+				out = append(out, " "+st.Error.Render(l))
+			}
+			return out
+		}
 		return []string{muted(" Select a vault or scope to browse its secrets.")}
 	}
 	c := *d.container