feat: support JSON import for test cases and add Traditional Chinese locale

JSON import lets users round-trip cases exported via the JSON download
endpoint back into a folder, alongside the existing Excel import path.

frontend/public/template/unittcms-import-sample.json

@@ -0,0 +1,33 @@
+[
+  {
+    "title": "User can sign in with valid credentials",
+    "priority": "high",
+    "type": "functional",
+    "template": "text",
+    "automationStatus": "automation-not-required",
+    "description": "Verify that a registered user can sign in.",
+    "preConditions": "A user account already exists.",
+    "expectedResults": "The user is redirected to the projects page after signing in.",
+    "Steps": []
+  },
+  {
+    "title": "Create a new project",
+    "priority": "medium",
+    "type": "acceptance",
+    "template": "step",
+    "automationStatus": "cannot-be-automated",
+    "description": "Verify that a signed-in user can create a project.",
+    "preConditions": "The user is signed in.",
+    "expectedResults": "The new project appears in the project list.",
+    "Steps": [
+      {
+        "step": "Click the \"New project\" button.",
+        "expectedStepResult": "The project creation dialog opens."
+      },
+      {
+        "step": "Enter a project name and submit.",
+        "expectedStepResult": "The dialog closes and the project is created."
+      }
+    ]
+  }
+]