feat: thumbnail grid, aspect-aware templates, and UI hierarchy polish

Material list:
- Switch asset list from one-per-row to a wrapping thumbnail grid
  (IconMode cards: thumbnail + corner checkbox + elided name, subfolder
  moved to tooltip).

Templates:
- Template.to_transform_state now contains-fits the print inside the
  target box by the print's native aspect ratio (no stretch); falls back
  to the box when print size is unknown.
- Feed print native size into template_panel for aspect-aware fitting.
- Shrink built-in template boxes to realistic print proportions.

UI hierarchy:
- Promote 打开文件夹 buttons to primary (filled accent).
- Add inline 归零 (reset angle) and a 重置位置/尺寸/角度 button to the
  transform panel; wire it to re-apply the selected template.
- Hide 保存 for built-in templates instead of leaving it greyed.

Docs: record template box/contain behavior (PRD) and the grid layout,
button hierarchy, and reset/save-visibility rules (UI design).
Tests: add 3 aspect-fit cases for to_transform_state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/core/models.py

@@ -59,13 +59,43 @@ class Template:
     rotation: float = 0.0
     type: str = "custom"         # "builtin" | "custom"
 
-    def to_transform_state(self, garment_width: float, garment_height: float) -> TransformState:
-        """将比例参数转换为针对指定衣服尺寸的像素坐标 TransformState。"""
+    def to_transform_state(
+        self,
+        garment_width: float,
+        garment_height: float,
+        print_width: float = None,
+        print_height: float = None,
+    ) -> TransformState:
+        """将比例参数转换为针对指定衣服尺寸的像素坐标 TransformState。
+
+        width_ratio / height_ratio 定义衣服上的目标框。若提供印花原始尺寸
+        (print_width / print_height)，印花按原始宽高比缩放后 contain 进目标框
+        并居中，避免被拉伸变形；未提供时退化为直接铺满目标框（旧行为）。
+        """
+        box_x = self.x_ratio * garment_width
+        box_y = self.y_ratio * garment_height
+        box_w = self.width_ratio * garment_width
+        box_h = self.height_ratio * garment_height
+
+        if print_width and print_height and print_width > 0 and print_height > 0:
+            scale = min(box_w / print_width, box_h / print_height)
+            draw_w = print_width * scale
+            draw_h = print_height * scale
+            cx = box_x + box_w / 2.0
+            cy = box_y + box_h / 2.0
+            return TransformState(
+                x=cx - draw_w / 2.0,
+                y=cy - draw_h / 2.0,
+                width=draw_w,
+                height=draw_h,
+                rotation=self.rotation,
+            )
+
         return TransformState(
-            x=self.x_ratio * garment_width,
-            y=self.y_ratio * garment_height,
-            width=self.width_ratio * garment_width,
-            height=self.height_ratio * garment_height,
+            x=box_x,
+            y=box_y,
+            width=box_w,
+            height=box_h,
             rotation=self.rotation,
         )