chore: disable Bevy default features to drop unused audio stack

Closes Quat investigation #2. The project uses kira for audio
(cpal 0.17 + alsa 0.10), but Bevy's default feature set still pulled
bevy_audio → rodio → cpal 0.15 + alsa 0.9 + symphonia codecs — about
50 transitive crates the binary never executes.

Workspace Cargo.toml's bevy entry now declares default-features =
false plus an explicit allow-list of the features actually used
(default_app subset + default_platform desktop subset + common_api +
2D + UI rendering). The list is derived analytically from the leaves
of Bevy 0.18's 2d and ui meta-features; built cleanly on the first
try with no missing-symbol errors.

Features intentionally omitted vs Bevy default:
- bevy_audio (kira handles audio directly)
- bevy_animation (custom CardAnimation, not Bevy's)
- bevy_gilrs, bevy_gizmos, bevy_picking variants, bevy_post_process,
  scene, hdr, sysinfo_plugin (none used)
- webgl2, web, android-* (desktop-only; solitaire_wasm is Bevy-free
  and uses wasm-bindgen + solitaire_core directly)
- wayland (X11 chosen; Wayland can be added later if requested)

Dependency-tree size for solitaire_app drops from 628 unique crates
to 577 (-51). Verified gone: bevy_audio, rodio, cpal 0.15. The
remaining cpal 0.17 and symphonia 0.5 are pulled by kira, not Bevy.

solitaire_wasm needed no changes — it doesn't depend on bevy.

All 1134 tests pass; clippy clean.

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

Cargo.toml

@@ -36,7 +36,46 @@ solitaire_sync   = { path = "solitaire_sync" }
 solitaire_data   = { path = "solitaire_data" }
 solitaire_engine = { path = "solitaire_engine" }
 
-bevy = "0.18"
+# Bevy with `default-features = false` to avoid the unused
+# `bevy_audio → rodio + symphonia + cpal 0.15 + alsa 0.9` chain.
+# Audio is handled directly by `kira` in `audio_plugin.rs`, so the
+# `bevy_audio` feature is intentionally omitted. The features below
+# enumerate every leaf of the standard `2d` + `ui` meta-features that
+# we actually use; new features should only be added with a
+# corresponding use site.
+bevy = { version = "0.18", default-features = false, features = [
+    # default_app
+    "async_executor",
+    "bevy_asset",
+    "bevy_input_focus",
+    "bevy_log",
+    "bevy_state",
+    "bevy_window",
+    "custom_cursor",
+    "reflect_auto_register",
+    # default_platform (desktop subset; no android/wayland/webgl/gilrs/sysinfo)
+    "std",
+    "bevy_winit",
+    "default_font",
+    "multi_threaded",
+    "x11",
+    # common_api
+    "bevy_color",
+    "bevy_image",
+    "bevy_mesh",
+    "bevy_shader",
+    "bevy_text",
+    "png",
+    # 2d rendering
+    "bevy_camera",
+    "bevy_render",
+    "bevy_core_pipeline",
+    "bevy_sprite",
+    "bevy_sprite_render",
+    # UI rendering
+    "bevy_ui",
+    "bevy_ui_render",
+] }
 kira = "0.12"
 
 # SVG rasterisation pipeline for the runtime card-theme system.