feat(web): add solitaire_web Bevy WASM build targeting play.html canvas

Adds a new `solitaire_web` crate that compiles the full `solitaire_engine`
to `wasm32-unknown-unknown` and renders to a `<canvas id="bevy-canvas">`
element in `play.html` — the same ECS code path as desktop and Android.

Changes to enable the WASM target:
- .cargo/config.toml: add wasm32-unknown-unknown rustflags for getrandom
- Workspace Cargo.toml: add solitaire_web member
- solitaire_data/Cargo.toml: gate tokio/reqwest/dirs/keyring to non-wasm
- solitaire_data/src: add wasm32 branch to data_dir() (returns None);
  cfg-gate sync_client network types, auth_tokens, matomo_client
- solitaire_engine/Cargo.toml: gate tokio/reqwest/kira/arboard/dirs/zip
  to non-wasm (mio/cpal/arboard don't compile for wasm32-unknown-unknown)
- solitaire_engine/src/lib.rs: cfg-gate module declarations and re-exports
  for analytics, audio, sync, sync_setup, avatar, leaderboard plugins
- solitaire_engine/src/core_game_plugin.rs: cfg-gate plugin registrations
  that require TokioRuntime (audio, sync, analytics, leaderboard, avatar)
- solitaire_engine/src/resources.rs: cfg-gate TokioRuntimeResource
- solitaire_engine/src/game_plugin.rs: cfg-gate std::fs::remove_file (x10)
- solitaire_engine/src/theme/mod.rs: cfg-gate importer module (uses dirs+zip)
- solitaire_engine/src/settings_plugin.rs: cfg-gate theme ZIP import UI
- solitaire_engine/src/assets/sources.rs: cfg-gate FileAssetReader/user_theme_dir
- solitaire_engine/src/auto_complete_plugin.rs: cfg-gate audio system
- solitaire_engine/src/daily_challenge_plugin.rs: cfg-gate server fetch
- solitaire_engine/src/hud_plugin.rs: cfg-gate AvatarResource import
- solitaire_engine/src/profile_plugin.rs: cfg-gate AvatarResource import
- solitaire_server/web/play.html: minimal HTML canvas shell
- solitaire_web/: new crate (Cargo.toml + src/lib.rs)
- build_wasm.sh: add Bevy WASM build step (cargo + wasm-bindgen + wasm-opt)

All tests pass; clippy --workspace -- -D warnings clean; native build
(solitaire_engine, solitaire_app) unaffected.

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

solitaire_engine/src/settings_plugin.rs

@@ -24,6 +24,7 @@ use solitaire_data::{
 
 use solitaire_data::settings::SyncBackend;
 
+#[cfg(not(target_arch = "wasm32"))]
 use crate::assets::user_theme_dir;
 use crate::events::{
     DeleteAccountRequestEvent, InfoToastEvent, ManualSyncRequestEvent, SyncConfigureRequestEvent,
@@ -32,9 +33,9 @@ use crate::events::{
 use crate::font_plugin::FontResource;
 use crate::progress_plugin::ProgressResource;
 use crate::resources::{SettingsScrollPos, SyncStatus, SyncStatusResource};
-use crate::theme::{
-    ImportError, ThemeThumbnailCache, ThemeThumbnailPair, import_theme, refresh_registry,
-};
+use crate::theme::{ThemeThumbnailCache, ThemeThumbnailPair, refresh_registry};
+#[cfg(not(target_arch = "wasm32"))]
+use crate::theme::{ImportError, import_theme};
 use crate::ui_focus::{FocusGroup, FocusRow, Focusable, FocusedButton};
 use crate::ui_modal::{
     ButtonVariant, ModalButton, ModalScrim, spawn_modal, spawn_modal_actions, spawn_modal_button,
@@ -404,6 +405,7 @@ impl Plugin for SettingsPlugin {
                     sync_settings_panel_visibility,
                     handle_settings_buttons,
                     handle_sync_buttons,
+                    #[cfg(not(target_arch = "wasm32"))]
                     handle_scan_themes,
                     update_sync_status_text,
                     update_card_back_text,
@@ -1857,6 +1859,7 @@ fn spawn_settings_panel(
                     font_res,
                 );
             }
+            #[cfg(not(target_arch = "wasm32"))]
             import_themes_row(body, font_res);
 
             // --- Privacy (only shown when a Matomo URL is configured) ---
@@ -2641,6 +2644,7 @@ fn value_text_font(font_res: Option<&FontResource>) -> TextFont {
 /// [`InfoToastEvent`] is fired per imported theme. `IdCollision` errors (theme
 /// already installed) are silently skipped; all other errors produce a warning
 /// toast. A final toast tells the player to reopen Settings to see new themes.
+#[cfg(not(target_arch = "wasm32"))]
 fn handle_scan_themes(
     interaction_query: Query<(&Interaction, &SettingsButton), Changed<Interaction>>,
     mut toast: MessageWriter<InfoToastEvent>,
@@ -2759,6 +2763,7 @@ fn pill_button(
 /// then presses the button. [`handle_scan_themes`] picks them up, validates,
 /// and installs them. Reopen Settings to see newly imported themes in the
 /// card-theme picker.
+#[cfg(not(target_arch = "wasm32"))]
 fn import_themes_row(parent: &mut ChildSpawnerCommands, font_res: Option<&FontResource>) {
     let caption_font = TextFont {
         font: font_res.map(|f| f.0.clone()).unwrap_or_default(),