polish(engine): standard empty/loading/error states (Phase L)

New ui_modal::spawn_empty_state — glyph + headline + optional detail,
centred, with next-step actions composed alongside rather than
configured in. Glyphs restricted to FiraMono-covered ranges (suits,
arrows, ASCII) per the section-10/11 Android constraint.

Swept every improvised surface onto it:
- Theme store: loading / error / empty-catalog branches
- Leaderboard: fetching / error / be-the-first branches
- You-hub Replays tab: dedicated no-replays state (selector and
  actions no longer spawn dead controls when history is empty)
- Stats: first-launch nudge above the em-dash grid

The Account tab's sync row was deliberately NOT swept: it is a live
status + action row, not an empty state, and its deeper treatment
belongs to Phase M's sync-transparency work.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/theme_store_plugin.rs

@@ -32,8 +32,8 @@ use crate::resources::TokioRuntimeResource;
 use crate::settings_plugin::{SettingsPanel, SettingsResource};
 use crate::theme::{ImportError, ThemeRegistry, import_theme, refresh_registry};
 use crate::ui_modal::{
-    ButtonVariant, ModalScrim, ScrimDismissible, spawn_modal, spawn_modal_actions,
-    spawn_modal_button, spawn_modal_header,
+    ButtonVariant, ModalScrim, ScrimDismissible, spawn_empty_state, spawn_modal,
+    spawn_modal_actions, spawn_modal_button, spawn_modal_header,
 };
 use crate::ui_theme::{
     BORDER_SUBTLE, TEXT_PRIMARY, TEXT_SECONDARY, TYPE_BODY, TYPE_CAPTION, VAL_SPACE_2, VAL_SPACE_3,
@@ -528,25 +528,31 @@ fn spawn_store_modal(
 
         match catalog_state {
             CatalogState::Idle | CatalogState::Loading => {
-                card.spawn((
-                    Text::new("Loading catalog…"),
-                    body_font.clone(),
-                    TextColor(TEXT_SECONDARY),
-                ));
+                spawn_empty_state(
+                    card,
+                    "\u{21BB}",
+                    "Loading the catalog\u{2026}",
+                    None,
+                    font_res,
+                );
             }
             CatalogState::Error(msg) => {
-                card.spawn((
-                    Text::new(format!("Could not load the catalog: {msg}")),
-                    body_font.clone(),
-                    TextColor(TEXT_SECONDARY),
-                ));
+                spawn_empty_state(
+                    card,
+                    "!",
+                    "Couldn't load the catalog.",
+                    Some(msg.as_str()),
+                    font_res,
+                );
             }
             CatalogState::Loaded(entries) if entries.is_empty() => {
-                card.spawn((
-                    Text::new("The server has no themes yet."),
-                    body_font.clone(),
-                    TextColor(TEXT_SECONDARY),
-                ));
+                spawn_empty_state(
+                    card,
+                    "#",
+                    "The server has no themes yet.",
+                    Some("Themes dropped into the server's theme_store folder appear here."),
+                    font_res,
+                );
             }
             CatalogState::Loaded(entries) => {
                 for entry in entries {