refactor: 重构目录结构，后端代码统一到 backend/ 目录

.gitea/workflows/go-loom.yaml

@@ -15,6 +15,9 @@ jobs:
   lint:
     name: Lint
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -34,6 +37,9 @@ jobs:
   test:
     name: Test
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -58,12 +64,15 @@ jobs:
         uses: actions/upload-artifact@v3
         with:
           name: coverage-report
-          path: coverage.out
+          path: backend/coverage.out
 
   build:
     name: Build
     runs-on: ubuntu-latest
     needs: [lint, test]
+    defaults:
+      run:
+        working-directory: backend
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -83,7 +92,7 @@ jobs:
         uses: actions/upload-artifact@v3
         with:
           name: goloom-server
-          path: goloom-server
+          path: backend/goloom-server
 
   # TODO: 添加 Dockerfile 后启用
   # docker: