ci: 移除CI配置中的offline特性

在CI配置中移除了`cargo test`和`cargo build`命令中的`--features offline`参数，以简化构建和测试流程，避免不必要的复杂性。

Author: ExquisiteCore

.github/workflows/backend.yml

@@ -44,7 +44,7 @@ jobs:
           DATABASE_URL: ${{ secrets.DATABASE_URL }}
           SQLX_OFFLINE: true
       - name: Run tests
-        run: cd backend && cargo test --verbose --features offline
+        run: cd backend && cargo test --verbose
 
   build:
     name: Build ${{ matrix.target.name }}
@@ -98,7 +98,7 @@ jobs:
       - name: Build release binary
         run: |
           cd backend
-          cargo build --release --target ${{ matrix.target.target }} --features offline
+          cargo build --release --target ${{ matrix.target.target }}
 
       - name: Prepare binary
         shell: bash