fix: resolve 3 CRITICAL + 5 MAJOR issues from Codex review

C1: Arc<Mutex<EventStore>> changed from tokio::sync to std::sync + spawn_blocking
C2: StateMachine::transition merged into single lock scope
C3: Transaction boundaries (BEGIN/COMMIT) on all composite writes
M4: retry_count no longer overwritten by update_task_status
M5: RetryPolicy::handle_failure now atomic (single lock + transaction)
M6: Per-task timeout_seconds used in SQL instead of global config
M7: Explicit Priority::order() method instead of relying on variant order
M8: dequeue_and_assign uses CAS-style WHERE status='created' for atomicity

src/main.rs

@@ -54,7 +54,7 @@ async fn main() {
     // Initialize event store
     let event_store = core::event_store::EventStore::open(std::path::Path::new(&config.orchestrator.db_path))
         .expect("failed to open event store");
-    let store = std::sync::Arc::new(tokio::sync::Mutex::new(event_store));
+    let store = std::sync::Arc::new(std::sync::Mutex::new(event_store));
 
     // Initialize core components
     let state_machine = std::sync::Arc::new(core::state_machine::StateMachine::new(store.clone()));