feat(engine): Phase M — sync transparency + local data backup

Closes out the 13-phase menu redesign. Three parts:

1. Post-sync merge summary: the pull poller now keeps the
   `ConflictReport`s the merge produces (previously discarded) in a new
   `SyncConflictLog` resource and toasts "Synced — N conflicts, kept
   newer values" when a merge wasn't clean. No wire changes — the
   server-side `SyncResponse.conflicts` field already existed.

2. Account tab detail: a per-field conflict list under the sync row
   ("win_streak_current — this device: 3 / server: 5") plus a
   clean-merge caption, so the last merge is always inspectable.

3. Local data export/import: new `solitaire_data::transfer` module —
   one versioned JSON bundle (settings, stats, achievements, progress)
   written atomically next to the other saves, with a version-gated
   loader that surfaces every failure instead of defaulting. Account
   tab grows an Export/Import button pair (desktop+Android only); the
   handler runs in `Last`, off the annotated Update spine. Import
   rewrites the live resources, persists via the existing save fns,
   and fires SettingsChangedEvent so appliers react normally.

Tests: bundle round-trip/version-gate/missing-file in solitaire_data;
ECS-level export→import round trip and failed-import-warns in
settings_plugin. Gate: workspace tests green, clippy -D warnings clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/settings_plugin/updates.rs

@@ -32,6 +32,7 @@ pub(super) fn sync_settings_panel_visibility(
     theme_registry: Option<Res<crate::theme::ThemeRegistry>>,
     theme_thumbs: Option<Res<ThemeThumbnailCache>>,
     card_images: Option<Res<crate::card_plugin::CardImageSet>>,
+    conflict_log: Option<Res<crate::resources::SyncConflictLog>>,
 ) {
     if !screen.is_changed() {
         return;
@@ -47,6 +48,7 @@ pub(super) fn sync_settings_panel_visibility(
                 theme_registry.as_deref(),
                 theme_thumbs.as_deref(),
                 card_images.as_deref(),
+                conflict_log.as_deref(),
                 scroll_pos.0,
                 active_tab.0,
             );
@@ -76,6 +78,7 @@ fn build_panel(
     theme_registry: Option<&crate::theme::ThemeRegistry>,
     theme_thumbs: Option<&ThemeThumbnailCache>,
     card_images: Option<&crate::card_plugin::CardImageSet>,
+    conflict_log: Option<&crate::resources::SyncConflictLog>,
     scroll_offset: f32,
     active_tab: SettingsTab,
 ) {
@@ -125,6 +128,7 @@ fn build_panel(
         scroll_offset,
         font_res,
         theme_overrides_back,
+        conflict_log,
         active_tab,
     );
 }
@@ -145,6 +149,7 @@ pub(super) fn rebuild_panel_on_tab_change(
     theme_registry: Option<Res<crate::theme::ThemeRegistry>>,
     theme_thumbs: Option<Res<ThemeThumbnailCache>>,
     card_images: Option<Res<crate::card_plugin::CardImageSet>>,
+    conflict_log: Option<Res<crate::resources::SyncConflictLog>>,
 ) {
     if !active_tab.is_changed() || active_tab.is_added() {
         return;
@@ -167,6 +172,7 @@ pub(super) fn rebuild_panel_on_tab_change(
         theme_registry.as_deref(),
         theme_thumbs.as_deref(),
         card_images.as_deref(),
+        conflict_log.as_deref(),
         0.0,
         active_tab.0,
     );