feat: auto-preview, timestamped/grouped output, folder memory; fix batch format

- Auto-preview the first image after a folder loads (both panels), so the
  canvas isn't empty (§17.8).
- Group exports as <output_dir>/<timestamp>/<print_stem>/<garment_stem>.<ext>;
  one timestamp per export run, shared across the batch (§17.9).
- Remember the last garment/print folders and reopen the picker there;
  persisted via config, wired through main_window (§17.10).
- Shrink the 3 box templates further and lower them (chest placement).
- Fix: batch export ignored the chosen format/quality/output dir because the
  queue never received ExportOptions. Export panel now emits
  export_options_changed → queue.set_export_options (+ initial sync) (§17.11).

Docs: PRD 6.1/6.8/9, architecture 4.12, UI design 5.1, tasks.md 17.8–17.11.

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

src/app/widgets/export_panel.py

@@ -2,7 +2,7 @@ import logging
 from pathlib import Path
 from typing import Optional
 
-from PySide6.QtCore import Qt
+from PySide6.QtCore import Qt, Signal
 from PySide6.QtWidgets import (
     QComboBox,
     QFileDialog,
@@ -17,7 +17,11 @@ from PySide6.QtWidgets import (
 
 from core.composer import compose
 from core.models import ExportOptions, TransformState
-from services.file_service import get_output_dir, make_safe_output_path
+from services.file_service import (
+    get_output_dir,
+    make_safe_output_path,
+    timestamped_run_dir,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -25,6 +29,8 @@ logger = logging.getLogger(__name__)
 class ExportPanel(QWidget):
     """Right-panel section: output settings and single-image export."""
 
+    export_options_changed = Signal(object)   # ExportOptions when dir/format/quality changes
+
     def __init__(self, parent=None):
         super().__init__(parent)
         self._garment_path: Optional[str] = None
@@ -66,6 +72,7 @@ class ExportPanel(QWidget):
         self._dir_input.setReadOnly(True)
         self._dir_input.setPlaceholderText("输出目录")
         self._dir_input.setText(str(get_output_dir()))
+        self._dir_input.textChanged.connect(self._emit_options)
 
         browse_btn = QPushButton("浏览…")
         browse_btn.setObjectName("exportBrowseBtn")
@@ -92,6 +99,7 @@ class ExportPanel(QWidget):
             self._quality_combo.addItem(label, val)
         self._quality_combo.setCurrentIndex(1)   # default: 高 (90)
         self._quality_combo.setEnabled(False)    # enabled only for JPG
+        self._quality_combo.currentIndexChanged.connect(self._emit_options)
 
         # 格式 and 质量 share one row (quality lights up only for JPG)
         row.addWidget(QLabel("格式"))
@@ -133,11 +141,24 @@ class ExportPanel(QWidget):
         """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()
+        return ExportOptions(
+            output_dir=self._dir_input.text().strip(),
+            output_format=fmt,
+            quality=self._quality_combo.currentData() if fmt == "JPG" else 95,
+        )
+
     # ── slot handlers ────────────────────────────────────────────────────────
 
+    def _emit_options(self, *_):
+        self.export_options_changed.emit(self.current_options())
+
     def _on_format_changed(self, _index: int):
         fmt = self._format_combo.currentData()
         self._quality_combo.setEnabled(fmt == "JPG")
+        self._emit_options()
 
     def _browse_output_dir(self):
         folder = QFileDialog.getExistingDirectory(
@@ -158,9 +179,8 @@ class ExportPanel(QWidget):
             QMessageBox.information(self, "提示", "当前没有可导出的印花参数。")
             return
 
-        out_dir = self._dir_input.text().strip() or str(get_output_dir())
-        fmt = self._format_combo.currentData()
-        quality = self._quality_combo.currentData() if fmt == "JPG" else 95
+        options = self.current_options()
+        out_dir = options.output_dir or str(get_output_dir())
 
         out_dir_path = Path(out_dir)
         try:
@@ -173,13 +193,10 @@ class ExportPanel(QWidget):
             )
             return
 
-        options = ExportOptions(
-            output_dir=out_dir,
-            output_format=fmt,
-            quality=quality,
-        )
+        # Group this export under a timestamped run folder (compose creates it)
+        run_dir = timestamped_run_dir(out_dir)
         output_path = make_safe_output_path(
-            out_dir, self._garment_path, self._print_path, fmt
+            run_dir, self._garment_path, self._print_path, options.output_format
         )
 
         result = compose(