fix(android): replace broken HUD glyphs and restore FiraMono font

‖ (U+2016) and ▾ (U+25BE) are absent from FiraMono and rendered as
boxes on device. Replace with || (ASCII) and ↓ (U+2193, Arrows block)
which are confirmed FiraMono-safe alongside the existing ≡ ← →.

Also removes the erroneous Android-only TextFont split introduced in
22303c6: that split accidentally used Bevy's built-in ASCII-only bitmap
font instead of FiraMono on Android, causing ALL non-ASCII HUD glyphs
to render as boxes. Now both platforms use the same FiraMono handle.

Separately, suppress the "Tab = next field" hint in the sync login
modal on Android (no Tab key on mobile).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/sync_setup_plugin.rs

@@ -673,7 +673,8 @@ fn spawn_sync_setup_modal(commands: &mut Commands, font_res: Option<&FontResourc
                 ));
             });
 
-            // Tab hint.
+            // Tab hint — desktop only; no Tab key on Android.
+            #[cfg(not(target_os = "android"))]
             body.spawn((
                 Text::new("Tab  =  next field"),
                 make_font(font_res, TYPE_CAPTION),