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>

Cargo.lock

@@ -5669,6 +5669,7 @@ name = "solitaire_app"
 version = "0.1.0"
 dependencies = [
  "bevy",
+ "solitaire_data",
  "solitaire_engine",
 ]
 
@@ -5707,11 +5708,15 @@ dependencies = [
 name = "solitaire_engine"
 version = "0.1.0"
 dependencies = [
+ "async-trait",
  "bevy",
  "chrono",
  "kira",
  "solitaire_core",
  "solitaire_data",
+ "solitaire_sync",
+ "tokio",
+ "uuid",
 ]
 
 [[package]]
@@ -5738,6 +5743,7 @@ dependencies = [
  "sqlx",
  "thiserror 1.0.69",
  "tokio",
+ "tower",
  "tower_governor",
  "tracing",
  "tracing-subscriber",
@@ -5751,6 +5757,7 @@ dependencies = [
  "chrono",
  "serde",
  "serde_json",
+ "thiserror 1.0.69",
  "uuid",
 ]