feat: add siegetank unit set and implement messaging system

- Created a new unit set for "siegetank" with various crew types and their attributes.
- Implemented a messaging system with types, payloads, and storage functionality.
- Added tests for the messaging system to ensure correct behavior for different message types (private, national, public, diplomacy).

app/game-api/src/messages/targets.ts

@@ -0,0 +1,50 @@
+import type { MessageTarget } from '@sammo-ts/logic';
+
+import type { DatabaseClient, GeneralRow } from '../context.js';
+
+const DEFAULT_NATION = {
+    name: '재야',
+    color: '#000000',
+};
+
+export const resolveNationInfo = async (
+    db: DatabaseClient,
+    nationId: number
+): Promise<{ name: string; color: string }> => {
+    if (nationId <= 0) {
+        return DEFAULT_NATION;
+    }
+    const nation = await db.nation.findUnique({ where: { id: nationId } });
+    if (!nation) {
+        return DEFAULT_NATION;
+    }
+    return { name: nation.name, color: nation.color };
+};
+
+export const buildTargetFromGeneral = async (
+    db: DatabaseClient,
+    general: GeneralRow
+): Promise<MessageTarget> => {
+    const nation = await resolveNationInfo(db, general.nationId);
+    return {
+        generalId: general.id,
+        generalName: general.name,
+        nationId: general.nationId,
+        nationName: nation.name,
+        color: nation.color,
+        icon: '',
+    };
+};
+
+export const buildNationTarget = (
+    nationId: number,
+    nationName: string,
+    color: string
+): MessageTarget => ({
+    generalId: 0,
+    generalName: '',
+    nationId,
+    nationName,
+    color,
+    icon: '',
+});