style: gofmt struct-tag alignment across v0 files

v0 landed with a few misaligned struct tags and fields; gofmt -l
flagged categories.go, topics.go, discourse_test.go and the smoke
fake. Alignment only, no behavior change, so the tree passes the
gofmt gate cleanly.

categories.go

@@ -28,13 +28,13 @@ type Category struct {
 // means "default: everyone full" — for restricted categories set it
 // explicitly, e.g. {"staff": 3, "trust_level_0": 1}.
 type CreateCategoryRequest struct {
-	Name              string         `json:"name"`
-	Color             string         `json:"color"`      // 6 hex digits, no '#'
-	TextColor         string         `json:"text_color"` // 6 hex digits, no '#'
-	Permissions       map[string]int `json:"permissions,omitempty"`
-	Position          int            `json:"position,omitempty"`
-	ParentCategoryID  int            `json:"parent_category_id,omitempty"`
-	Description       string         `json:"description,omitempty"`
+	Name             string         `json:"name"`
+	Color            string         `json:"color"`      // 6 hex digits, no '#'
+	TextColor        string         `json:"text_color"` // 6 hex digits, no '#'
+	Permissions      map[string]int `json:"permissions,omitempty"`
+	Position         int            `json:"position,omitempty"`
+	ParentCategoryID int            `json:"parent_category_id,omitempty"`
+	Description      string         `json:"description,omitempty"`
 }
 
 // ListCategories returns the instance's categories (one request; the