feat(workspace): full server + sync implementation, all tests green

- solitaire_server: Axum auth, sync push/pull, leaderboard, daily
  challenge, account deletion, JWT middleware, rate limiting via
  tower_governor, SQLite migrations, health endpoint
- solitaire_server: expose build_test_router (no rate limiting) so
  integration tests work without a peer IP in oneshot requests
- solitaire_sync: SyncPayload, merge logic, shared API types
- solitaire_data: SyncProvider trait, LocalOnlyProvider,
  SolitaireServerClient, auth_tokens keyring integration, blanket
  Box<dyn SyncProvider> impl
- solitaire_data/settings: derive Default on SyncBackend (clippy fix)
- .sqlx/: offline query cache so server compiles without a live DB
- sqlx: removed non-existent "offline" feature flag
- keyring v2: fixed Entry::new() returning Result<Entry>
- sqlx 0.8: all SQLite TEXT columns wrapped in Option<T>
- Integration tests: max_connections(1) on in-memory pool so all
  connections share the same schema

All 191 tests pass; cargo clippy -D warnings clean.

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

solitaire_engine/src/lib.rs

@@ -17,6 +17,7 @@ pub mod settings_plugin;
 pub mod progress_plugin;
 pub mod resources;
 pub mod stats_plugin;
+pub mod sync_plugin;
 pub mod table_plugin;
 pub mod time_attack_plugin;
 pub mod weekly_goals_plugin;
@@ -43,11 +44,12 @@ pub use input_plugin::InputPlugin;
 pub use onboarding_plugin::{OnboardingPlugin, OnboardingScreen};
 pub use pause_plugin::{PausePlugin, PauseScreen, PausedResource};
 pub use settings_plugin::{
-    SettingsChangedEvent, SettingsPlugin, SettingsResource, SFX_STEP,
+    SettingsChangedEvent, SettingsPlugin, SettingsResource, SettingsScreen, SFX_STEP,
 };
 pub use layout::{compute_layout, Layout, LayoutResource};
 pub use resources::{DragState, GameStateResource, SyncStatus, SyncStatusResource};
 pub use stats_plugin::{StatsPlugin, StatsResource, StatsScreen, StatsUpdate};
+pub use sync_plugin::{SyncPlugin, SyncProviderResource};
 pub use table_plugin::{PileMarker, TableBackground, TablePlugin};
 pub use time_attack_plugin::{
     TimeAttackEndedEvent, TimeAttackPlugin, TimeAttackResource, TIME_ATTACK_DURATION_SECS,