feat: add image folder scanning and safe output filename

- scan_image_folder(): recursively scans a directory for supported
  images (png/jpg/jpeg/webp, case-insensitive), returns List[ImageAsset],
  skips and logs unsupported files, raises OSError on bad path
- make_safe_output_path(): builds <garment>_<print>.<ext> filename,
  appends _1/_2/... counter if destination already exists

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/file_service.py

@@ -1,6 +1,7 @@
 import logging
 import sys
 from pathlib import Path
+from typing import List
 
 logger = logging.getLogger(__name__)
 
@@ -8,7 +9,8 @@ SUPPORTED_IMAGE_EXTENSIONS = {".png", ".jpg", ".jpeg", ".webp"}
 
 
 def is_supported_image(path):
-    return path.suffix.lower() in SUPPORTED_IMAGE_EXTENSIONS
+    """Return True if path has a supported image extension (case-insensitive)."""
+    return Path(path).suffix.lower() in SUPPORTED_IMAGE_EXTENSIONS
 
 
 # ---------------------------------------------------------------------------
@@ -49,3 +51,65 @@ def get_output_dir():
     d = get_app_dir() / "output"
     d.mkdir(exist_ok=True)
     return d
+
+
+# ---------------------------------------------------------------------------
+# 文件夹扫描
+# ---------------------------------------------------------------------------
+
+def scan_image_folder(folder) -> List:
+    """Recursively scan *folder* for supported images.
+
+    Returns a list of ImageAsset objects (selected=True by default).
+    Skips unsupported files and logs them at DEBUG level.
+    Raises OSError if *folder* does not exist or is not a directory.
+    """
+    from core.models import ImageAsset
+
+    folder = Path(folder)
+    if not folder.exists():
+        raise OSError("Folder not found: {}".format(folder))
+    if not folder.is_dir():
+        raise OSError("Path is not a directory: {}".format(folder))
+
+    assets = []
+    skipped_count = 0
+
+    for entry in sorted(folder.rglob("*")):
+        if not entry.is_file():
+            continue
+        if is_supported_image(entry):
+            assets.append(ImageAsset(path=entry))
+        else:
+            skipped_count += 1
+            logger.debug("Skipped unsupported file: %s", entry)
+
+    if skipped_count:
+        logger.info(
+            "Skipped %d unsupported file(s) in %s", skipped_count, folder
+        )
+    logger.info("Found %d image(s) in %s", len(assets), folder)
+    return assets
+
+
+# ---------------------------------------------------------------------------
+# 安全输出文件名
+# ---------------------------------------------------------------------------
+
+def make_safe_output_path(output_dir, garment_path, print_path, output_format="PNG"):
+    """Return an output Path that will not overwrite an existing file.
+
+    Filename pattern : <garment_stem>_<print_stem>.<ext>
+    If that path exists, appends _1, _2, ... until a free slot is found.
+    """
+    output_dir = Path(output_dir)
+    ext = ".png" if output_format.upper() == "PNG" else ".jpg"
+    stem = "{}_{}".format(Path(garment_path).stem, Path(print_path).stem)
+
+    candidate = output_dir / (stem + ext)
+    counter = 1
+    while candidate.exists():
+        candidate = output_dir / ("{}_{}{}".format(stem, counter, ext))
+        counter += 1
+
+    return candidate