Add comprehensive kanban board tests and fix test suite

- Add 13 tests for task kanban categorization and button types
- Fix i18n initialization in test setup (was causing nil pointer panics)
- Add TaskCompletionImage to test DB auto-migrate
- Update ListTasks tests to expect kanban board response instead of array

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/handlers/task_handler_test.go

@@ -168,11 +168,23 @@ func TestTaskHandler_ListTasks(t *testing.T) {
 
 		testutil.AssertStatusCode(t, w, http.StatusOK)
 
-		var response []map[string]interface{}
+		// ListTasks returns a kanban board object, not an array
+		var response map[string]interface{}
 		err := json.Unmarshal(w.Body.Bytes(), &response)
 		require.NoError(t, err)
 
-		assert.Len(t, response, 3)
+		// Verify kanban structure
+		assert.Contains(t, response, "columns")
+		assert.Contains(t, response, "days_threshold")
+
+		// Count total tasks across all columns
+		columns := response["columns"].([]interface{})
+		totalTasks := 0
+		for _, col := range columns {
+			column := col.(map[string]interface{})
+			totalTasks += int(column["count"].(float64))
+		}
+		assert.Equal(t, 3, totalTasks)
 	})
 }
 
@@ -651,16 +663,19 @@ func TestTaskHandler_JSONResponses(t *testing.T) {
 		assert.IsType(t, false, response["is_archived"])
 	})
 
-	t.Run("list response returns array", func(t *testing.T) {
+	t.Run("list response returns kanban board", func(t *testing.T) {
 		w := testutil.MakeRequest(router, "GET", "/api/tasks/", nil, "test-token")
 
 		testutil.AssertStatusCode(t, w, http.StatusOK)
 
-		var response []map[string]interface{}
+		// ListTasks returns a kanban board object with columns
+		var response map[string]interface{}
 		err := json.Unmarshal(w.Body.Bytes(), &response)
 		require.NoError(t, err)
 
-		// Response should be an array of tasks
-		assert.IsType(t, []map[string]interface{}{}, response)
+		// Response should be a kanban board object
+		assert.Contains(t, response, "columns")
+		assert.Contains(t, response, "days_threshold")
+		assert.IsType(t, []interface{}{}, response["columns"])
 	})
 }