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/app/main_window.py

@@ -269,6 +269,9 @@ class MainWindow(QMainWindow):
         self.image_canvas.transform_changed.connect(self._on_transform_changed)
         self.transform_panel.transform_changed.connect(self._on_transform_changed)
 
+        # Reset position/size/angle back to the selected template
+        self.transform_panel.reset_to_template.connect(self.template_panel._reset_to_template)
+
         # ── Template panel ─────────────────────────────────────────────────
         # Template selection updates canvas, param panel, and queue template
         self.template_panel.template_applied.connect(self.image_canvas.set_transform)
@@ -305,6 +308,13 @@ class MainWindow(QMainWindow):
         path = str(asset.path)
         self.image_canvas.load_print(path)
         self.export_panel.set_print(path)
+        # Tell template panel the print dimensions for aspect-aware fitting
+        try:
+            from PIL import Image as _PilImage
+            with _PilImage.open(path) as img:
+                self.template_panel.set_print_size(img.width, img.height)
+        except Exception:
+            pass
 
     def _on_queue_item_activated(self, item):
         """Load a queue item into the canvas and arm fine-tune tracking."""
@@ -321,11 +331,13 @@ class MainWindow(QMainWindow):
             if item.transform:
                 self.image_canvas.set_transform(item.transform)
                 self.transform_panel.set_transform(item.transform)
-            # Keep template panel garment size in sync
+            # Keep template panel garment and print size in sync
             try:
                 from PIL import Image as _PilImage
                 with _PilImage.open(garment_path) as img:
                     self.template_panel.set_garment_size(img.width, img.height)
+                with _PilImage.open(print_path) as img:
+                    self.template_panel.set_print_size(img.width, img.height)
             except Exception:
                 pass
         finally: