refactor(banking-demo): introduce DemoApplication orchestrator and add controlled lifecycle management

- Replace DemoFactory with DemoApplication to centralize system setup, execution, and shutdown
- Move ExecutorService and ScheduledExecutorService lifecycle management into application layer
- Ensure proper shutdown sequence for worker and monitoring threads
- Simplify Main class to a minimal entry-point wrapper
- Improve clarity of execution flow: build → run → shutdown
- Prevent resource leakage by explicitly awaiting termination of thread pools

src/main/java/dev/banking/DemoApplication.java

@@ -0,0 +1,108 @@
+package dev.banking;
+
+import dev.banking.model.*;
+import dev.banking.monitor.LiveMonitor;
+import dev.banking.processor.TransactionProcessor;
+import dev.banking.service.BankingSystem;
+
+import java.util.*;
+import java.util.concurrent.*;
+
+/**
+ * DemoApplication is responsible for:
+ * - Building the system
+ * - Running the simulation
+ * - Managing lifecycle (threads, schedulers)
+ *
+ * This class replaces DemoFactory as a full runner.
+ */
+public final class DemoApplication {
+
+    private DemoApplication() {
+    }
+
+    public static void run() {
+
+        System.out.println("Initializing Banking Simulation...\n");
+
+        /*
+         * 1. Create bank accounts
+         */
+        BankAccount acc1 = new BankAccount(1, 1000);
+        BankAccount acc2 = new BankAccount(2, 2000);
+        BankAccount acc3 = new BankAccount(3, 1500);
+
+        Map<Integer, BankAccount> accounts = new HashMap<>();
+        accounts.put(1, acc1);
+        accounts.put(2, acc2);
+        accounts.put(3, acc3);
+
+        /*
+         * 2. Create transactions
+         */
+        List<Transaction> transactions = List.of(
+                new DepositTransaction(1, 200),
+                new WithdrawTransaction(2, 300),
+                new TransferTransaction(1, 2, 150),
+                new TransferTransaction(2, 3, 400),
+                new DepositTransaction(3, 500),
+                new WithdrawTransaction(1, 100),
+                new TransferTransaction(3, 1, 250)
+        );
+
+        /*
+         * 3. Thread pool (workers)
+         */
+        ExecutorService executor = Executors.newFixedThreadPool(4);
+
+        /*
+         * 4. Processor
+         */
+        TransactionProcessor processor = new TransactionProcessor(accounts);
+
+        /*
+         * 5. Banking system
+         */
+        BankingSystem bankingSystem = new BankingSystem(executor, processor);
+
+        /*
+         * 6. Live monitor (UI simulation)
+         */
+        LiveMonitor monitor = new LiveMonitor();
+
+        ScheduledExecutorService monitorExecutor = Executors.newSingleThreadScheduledExecutor();
+
+        monitorExecutor.scheduleAtFixedRate(() -> {
+            monitor.update(accounts.values());
+            System.out.println("----------------------");
+        }, 0, 1, TimeUnit.SECONDS);
+
+        /*
+         * 7. Run simulation
+         */
+        bankingSystem.processTransactions(transactions);
+
+        /*
+         * 8. Shutdown / lifecycle management
+         */
+        shutdown(executor, monitorExecutor);
+
+        System.out.println("\nSimulation completed.");
+    }
+
+    private static void shutdown(
+            ExecutorService executor,
+            ScheduledExecutorService monitorExecutor
+    ) {
+        try {
+            executor.shutdown();
+            executor.awaitTermination(5, TimeUnit.SECONDS);
+
+            monitorExecutor.shutdown();
+            monitorExecutor.awaitTermination(5, TimeUnit.SECONDS);
+
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}