Fixes found while testing the Bevy WASM build in a real browser:
1. chrono wasmbind: add `wasmbind` feature to workspace chrono dep so
Local::now()/Utc::now() use js-sys::Date on wasm32 (previously
fell through to std::time::SystemTime which panics on wasm32).
2. std::time::SystemTime: replace all remaining direct SystemTime::now()
calls (4 sites across game_plugin, difficulty_plugin, time_attack_plugin,
solitaire_data/storage) with chrono::Utc::now() which is wasm32-safe.
3. user_dir: return empty PathBuf (instead of panicking) when data_dir()
is None on wasm32; there is no filesystem in the browser so user themes
are unsupported and a benign empty path is correct.
4. ThemeRegistryPlugin: gate build_registry_on_startup to non-wasm32
(the filesystem scan for user themes has nothing to scan in the browser;
only the bundled embedded themes are available).
5. AssetMetaCheck::Never: configure AssetPlugin in solitaire_web to skip
`.meta` sidecar fetches — we don't ship .meta files, so the default
AssetMetaCheck::Always produced a 404 flood on every card/background asset.
Result: `http://localhost:<port>/play` boots in Firefox with zero errors
and renders the full Bevy game — home screen, onboarding modal, HUD all
visible. Assets load correctly from /assets/. Chromium has a separate
wgpu-27/ANGLE/GLES shader translation bug (not in our code); Firefox works.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>