feat: print name in output filename; export panel trim; queue template fix

- Output filename now includes the print: <garment>_<print>.<ext>, e.g.
  1_TY030.png (folder grouping unchanged) (§17.12).
- Hide the single-export button (export via the queue) and remove the
  orphaned static export hint label (§17.13).
- Fix: selecting a non-fine-tuned queue item now lays the print out per the
  selected template (apply_current) instead of load_print's centred default;
  still guarded by _loading_queue_item so it isn't marked 已微调 (§17.14).

Docs: PRD 6.6/6.8/9, UI design 7.6/7.7/10/12.4, tasks.md 17.12–17.14.

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

src/app/widgets/export_panel.py

@@ -58,7 +58,6 @@ class ExportPanel(QWidget):
 
         body_col.addLayout(self._make_dir_row())
         body_col.addLayout(self._make_format_form())
-        body_col.addWidget(self._make_hint_label())
         body_col.addWidget(self._make_export_btn())
 
         col.addWidget(body)
@@ -108,16 +107,11 @@ class ExportPanel(QWidget):
         row.addWidget(self._quality_combo, 1)
         return row
 
-    def _make_hint_label(self) -> QLabel:
-        self._hint_lbl = QLabel("加载衣服和印花图片后即可导出。")
-        self._hint_lbl.setObjectName("exportHint")
-        self._hint_lbl.setWordWrap(True)
-        return self._hint_lbl
-
     def _make_export_btn(self) -> QPushButton:
         self._export_btn = QPushButton("导出当前单张")
         self._export_btn.setObjectName("exportPrimaryBtn")
         self._export_btn.setEnabled(False)
+        self._export_btn.setVisible(False)   # hidden: export via the queue
         self._export_btn.clicked.connect(self._do_export)
         return self._export_btn
 
@@ -137,10 +131,6 @@ class ExportPanel(QWidget):
         """Store current print transform (used on export)."""
         self._transform = state
 
-    def set_hint(self, text: str):
-        """Update the operation-scope hint label."""
-        self._hint_lbl.setText(text)
-
     def current_options(self) -> ExportOptions:
         """Build ExportOptions from the current output settings."""
         fmt = self._format_combo.currentData()
@@ -256,14 +246,6 @@ class ExportPanel(QWidget):
                 border-radius: 3px;
                 padding: 2px 4px;
             }
-            #exportHint {
-                font-size: 11px;
-                color: #777777;
-                background: #fffbe6;
-                border: 1px solid #ffe58f;
-                border-radius: 3px;
-                padding: 4px 6px;
-            }
             #exportPrimaryBtn {
                 font-family: "Microsoft YaHei", "Segoe UI", sans-serif;
                 font-size: 13px;