fix(engine): silence usvg font-substitution warn spam

The bundled hayeah card SVGs declare font-family="Arial" for rank/suit
text. usvg matches family names exactly, so on systems without Arial
installed (every Linux distro by default) every text node bridged a
log::warn! into our tracing output — 50+ lines per launch.

Two-part fix:
- svg_loader now populates a process-wide fontdb with system fonts
  (lazy via OnceLock) so substitution actually has faces to fall
  through to. usvg::Options::default() ships an empty fontdb, which
  meant text glyphs had nothing to fall back on at all.
- LogPlugin extends DEFAULT_FILTER with usvg::text=error so the
  residual "no match" warns drop. The substitution itself works; the
  message is purely informational because Arial truly isn't installed.

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

solitaire_app/src/main.rs

@@ -100,6 +100,19 @@ fn main() {
                 .set(bevy::asset::AssetPlugin {
                     file_path: "../assets".to_string(),
                     ..default()
+                })
+                // The bundled hayeah card SVGs declare `font-family="Arial"`
+                // for rank/suit text. usvg compares family names exactly,
+                // so on systems without Arial installed (every Linux
+                // distro by default) it bridges a `log::warn!` per text
+                // node into our tracing output — 50+ lines per game on
+                // launch. The substitution path in `svg_loader::shared_fontdb`
+                // already resolves the glyphs to whatever sans-serif the
+                // user does have; the warn is purely informational and
+                // dropping it leaves real errors visible.
+                .set(bevy::log::LogPlugin {
+                    filter: format!("{},usvg::text=error", bevy::log::DEFAULT_FILTER),
+                    ..default()
                 }),
         )
         .add_plugins(AssetSourcesPlugin)