feat(engine): first-launch polish — em-dash zero stats and welcome line on profile

On first launch the Stats grid previously mixed "0" cells (Games
Played / Won / Lost) with "—" cells (Best Score / Win Rate / Avg
Time), reading as inconsistent. Now every cell renders an em-dash
when games_played == 0, and a "Play a game to start tracking stats."
caption sits above the grid using the existing TYPE_CAPTION /
TEXT_SECONDARY tokens. Once a game has been played the original
formatters resume.

The Profile screen gains a one-line welcome ("Welcome! Play games to
earn XP and unlock achievements.") that renders only when both
total_xp and the daily streak are zero, breaking up the wall of
zero-valued readouts that greeted users on first launch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

solitaire_engine/src/profile_plugin.rs

@@ -111,6 +111,27 @@ fn spawn_profile_screen(
     spawn_modal(commands, ProfileScreen, Z_MODAL_PANEL, |card| {
         spawn_modal_header(card, "Profile", font_res);
 
+        // First-launch welcome — only when the player has zero XP and
+        // zero daily streak, so the profile doesn't read as a wall of
+        // zeros to a brand-new player.
+        if let Some(p) = progress
+            && p.0.total_xp == 0
+            && p.0.daily_challenge_streak == 0
+        {
+            card.spawn((
+                Text::new("Welcome! Play games to earn XP and unlock achievements."),
+                font_section.clone(),
+                TextColor(ACCENT_PRIMARY),
+                Node {
+                    margin: UiRect {
+                        bottom: VAL_SPACE_2,
+                        ..default()
+                    },
+                    ..default()
+                },
+            ));
+        }
+
         // ── Sync section ────────────────────────────────────────────
         card.spawn((
             Text::new("Sync"),