feat(themes): warn about animated themes on high-CPU setups (#1020)

* feat(themes): warn about animated themes on high-CPU setups

Show a warning icon + tooltip on animated themes (those defining
@keyframes) in the store and in Your Themes, on Linux setups where
animation is costly — the Nvidia WebKit quirk is active or compositing
is forced off. The Nvidia detection already runs once at startup; its
result is recorded (theme_animation.rs) and read via a new
theme_animation_risk command — no GPU re-probe. Display-only; never
shown off Linux. The animated flag comes from the registry (store) or
the theme CSS (Your Themes).

* docs(themes): note the animated-theme warning PR in the Theme Store entry

src-tauri/src/lib.rs

@@ -6,6 +6,7 @@ mod cover_cache;
 mod library_analysis_backfill;
 mod lib_commands;
 mod theme_import;
+pub mod theme_animation;
 
 pub use psysonic_integration::discord;
 
@@ -653,6 +654,7 @@ pub fn run() {
             performance_cpu_snapshot,
             set_subsonic_wire_user_agent,
             no_compositing_mode,
+            theme_animation_risk,
             linux_xdg_session_type,
             is_tiling_wm_cmd,
             open_mini_player,