Add custom folder support and improve image loading for multi-vector … (#188)

* Add custom folder support and improve image loading for multi-vector retrieval

- Enhanced _load_images_from_dir with recursive search support and better error handling
- Added support for WebP format and RGB conversion for all image modes
- Added custom folder CLI arguments (--custom-folder, --recursive, --rebuild-index)
- Improved documentation and removed completed TODO comment

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* Format code style in leann_multi_vector.py for better readability

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/multimodal/vision-based-pdf-multi-vector/leann_multi_vector.py

@@ -1,4 +1,5 @@
 import concurrent.futures
+import glob
 import json
 import os
 import re
@@ -96,12 +97,63 @@ def _natural_sort_key(name: str) -> int:
     return int(m.group()) if m else 0
 
 
-def _load_images_from_dir(pages_dir: str) -> tuple[list[str], list[Image.Image]]:
-    filenames = [n for n in os.listdir(pages_dir) if n.lower().endswith((".png", ".jpg", ".jpeg"))]
-    filenames = sorted(filenames, key=_natural_sort_key)
-    filepaths = [os.path.join(pages_dir, n) for n in filenames]
-    images = [Image.open(p) for p in filepaths]
-    return filepaths, images
+def _load_images_from_dir(
+    pages_dir: str, recursive: bool = False
+) -> tuple[list[str], list[Image.Image]]:
+    """
+    Load images from a directory.
+
+    Args:
+        pages_dir: Directory path containing images
+        recursive: If True, recursively search subdirectories (default: False)
+
+    Returns:
+        Tuple of (filepaths, images)
+    """
+
+    # Supported image extensions
+    extensions = ("*.png", "*.jpg", "*.jpeg", "*.PNG", "*.JPG", "*.JPEG", "*.webp", "*.WEBP")
+
+    if recursive:
+        # Recursive search
+        filepaths = []
+        for ext in extensions:
+            pattern = os.path.join(pages_dir, "**", ext)
+            filepaths.extend(glob.glob(pattern, recursive=True))
+    else:
+        # Non-recursive search (only top-level directory)
+        filepaths = []
+        for ext in extensions:
+            pattern = os.path.join(pages_dir, ext)
+            filepaths.extend(glob.glob(pattern))
+
+    # Sort files naturally
+    filepaths = sorted(filepaths, key=lambda x: _natural_sort_key(os.path.basename(x)))
+
+    # Load images with error handling
+    images = []
+    valid_filepaths = []
+    failed_count = 0
+
+    for filepath in filepaths:
+        try:
+            img = Image.open(filepath)
+            # Convert to RGB if necessary (handles RGBA, P, etc.)
+            if img.mode != "RGB":
+                img = img.convert("RGB")
+            images.append(img)
+            valid_filepaths.append(filepath)
+        except Exception as e:
+            failed_count += 1
+            print(f"Warning: Failed to load image {filepath}: {e}")
+            continue
+
+    if failed_count > 0:
+        print(
+            f"Warning: Failed to load {failed_count} image(s) out of {len(filepaths)} total files"
+        )
+
+    return valid_filepaths, images
 
 
 def _maybe_convert_pdf_to_images(pdf_path: Optional[str], pages_dir: str, dpi: int = 200) -> None: