refactor: 重构所有面板 update_from_config 为文件系统扫描模式

=== 核心变更 ===
- _step_path_resolver 新增 scan_work_dir_for_input() 统一文件扫描工具
- 基于 _SCAN_TABLE 映射表，按 output_type 自动扫描 work_dir 子目录
- 支持扩展名匹配（.dat/.tif/.bsq/.csv 等）和文件名关键词匹配
- 按 mtime 排序，返回最新匹配文件

=== 各面板重构 ===
- step2/3/4/6: 废弃 main_window.stepX_panel 跨面板读取
  统一改为 scan_work_dir_for_input(work_dir, 'water_mask/glint_mask/deglint_image')
- step6: 移除对 step1/2/3/5 panel 的4处跨面板依赖
- step8: 替换 _resolve_training_csv_from_workdir 为 scan_work_dir_for_input
  优先级：training_spectra_indices -> training_spectra
- step9: 替换 _resolve_latest_wqi_test_csv 为 scan_work_dir_for_input
  废弃 factory.get_panel('step4_sampling') 和 get_panel('step8_ml_train')
- step10: 替换3层回退链为 scan_work_dir_for_input('sampling_points')
- step11: 替换 factory.get_panel('step9')/('step1') 为文件扫描

=== 删除的冗余方法 ===
- step8._resolve_training_csv_from_workdir (~55行)
- step9._resolve_latest_wqi_test_csv (~56行)

=== 数据流原则 ===
1. pipeline context 为第一顺位（执行时内存状态）
2. 文件系统扫描为回退（仅信任硬盘上真实存在的文件）
3. 彻底禁止面板间 UI 控件互相读取

src/gui/panels/step3_panel.py

@@ -11,7 +11,7 @@ from pathlib import Path
 _HERE = os.path.dirname(os.path.abspath(__file__))
 if _HERE not in sys.path:
     sys.path.insert(0, _HERE)
-from _step_path_resolver import resolve_subdir
+from _step_path_resolver import resolve_subdir, scan_work_dir_for_input
 
 from PyQt5.QtWidgets import (
     QWidget, QVBoxLayout, QHBoxLayout, QGroupBox, QFormLayout,
@@ -307,20 +307,23 @@ class Step3Panel(QWidget):
         else:
             self.work_dir = None
 
-        main_window = self.window()
-        if hasattr(main_window, 'step1_panel'):
-            if main_window.step1_panel.use_ndwi_radio.isChecked():
-                mask_path = main_window.step1_panel.output_file.get_path()
-            else:
-                mask_path = main_window.step1_panel.mask_file.get_path()
+        # ── 水域掩膜输入 ──
+        # 优先：pipeline context
+        mask_path = None
+        if pipeline and hasattr(pipeline, 'step_outputs'):
+            step1_out = pipeline.step_outputs.get('step1', {})
+            mask_path = step1_out.get('water_mask') or step1_out.get('output_path')
 
-            if mask_path:
-                if not os.path.isabs(mask_path):
-                    mask_path = os.path.join(self.work_dir or '', mask_path).replace('\\', '/')
-                # 仅当上游文件确实存在时才自动填入（防止幽灵路径级联扩散）
-                if os.path.exists(mask_path):
-                    self.water_mask_file.set_path(mask_path)
+        # 回退：文件系统扫描 1_water_mask/
+        if not mask_path or not os.path.exists(mask_path):
+            mask_path = scan_work_dir_for_input(self.work_dir, 'water_mask')
 
+        if mask_path and os.path.exists(mask_path):
+            if not os.path.isabs(mask_path):
+                mask_path = os.path.join(self.work_dir or '', mask_path).replace('\\', '/')
+            self.water_mask_file.set_path(mask_path)
+
+        # ── 输出路径 ──
         if self.work_dir:
             if not self.output_file.get_path():
                 output_dir = resolve_subdir(self.work_dir, 'deglint')