feat: Enhance tag management in TagSelectedPhotosDialog with improved logic for removable tags

This commit updates the TagSelectedPhotosDialog to allow both single and bulk tags to be managed more effectively. The logic for determining removable tags has been refined, ensuring that users can see which tags are common across selected photos and whether they can be removed. Additionally, the photo date extraction method in PhotoManager has been improved to include a fallback to file modification time, enhancing reliability. The photo service now also utilizes this updated method for date extraction, ensuring consistency across the application. Documentation has been updated to reflect these changes.

src/core/photo_management.py

@@ -23,16 +23,22 @@ class PhotoManager:
         self.verbose = verbose
     
     def extract_photo_date(self, photo_path: str) -> Optional[str]:
-        """Extract date taken from photo EXIF data"""
+        """Extract date taken from photo with fallback to file modification time.
+        
+        Tries in order:
+        1. EXIF date tags (DateTimeOriginal, DateTimeDigitized, DateTime)
+        2. File modification time (as fallback)
+        """
+        # First try EXIF date extraction
         try:
             with Image.open(photo_path) as image:
                 exifdata = image.getexif()
                 
                 # Look for date taken in EXIF tags
                 date_tags = [
-                    306,  # DateTime
-                    36867,  # DateTimeOriginal
-                    36868,  # DateTimeDigitized
+                    36867,  # DateTimeOriginal - when photo was actually taken (highest priority)
+                    36868,  # DateTimeDigitized - when photo was digitized
+                    306,  # DateTime - file modification date (lowest priority)
                 ]
                 
                 for tag_id in date_tags:
@@ -50,12 +56,21 @@ class PhotoManager:
                                     return date_obj.strftime('%Y-%m-%d')
                                 except ValueError:
                                     continue
-                
-                return None
         except Exception as e:
             if self.verbose >= 2:
-                print(f"   ⚠️  Could not extract date from {os.path.basename(photo_path)}: {e}")
-            return None
+                print(f"   ⚠️  Could not extract EXIF date from {os.path.basename(photo_path)}: {e}")
+        
+        # Fallback to file modification time
+        try:
+            if os.path.exists(photo_path):
+                mtime = os.path.getmtime(photo_path)
+                mtime_date = datetime.fromtimestamp(mtime)
+                return mtime_date.strftime('%Y-%m-%d')
+        except Exception as e:
+            if self.verbose >= 2:
+                print(f"   ⚠️  Could not get file modification time from {os.path.basename(photo_path)}: {e}")
+        
+        return None
     
     def scan_folder(self, folder_path: str, recursive: bool = True) -> int:
         """Scan folder for photos and add to database"""

src/web/services/photo_service.py

@@ -102,6 +102,36 @@ def extract_exif_date(image_path: str) -> Optional[date]:
     return None
 
 
+def extract_photo_date(image_path: str) -> Optional[date]:
+    """Extract date taken from photo with fallback to file modification time.
+    
+    Tries in order:
+    1. EXIF date tags (DateTimeOriginal, DateTimeDigitized, DateTime)
+    2. File modification time (as fallback)
+    
+    Returns:
+        Date object or None if no date can be determined
+    """
+    # First try EXIF date extraction
+    date_taken = extract_exif_date(image_path)
+    if date_taken:
+        return date_taken
+    
+    # Fallback to file modification time
+    try:
+        if os.path.exists(image_path):
+            mtime = os.path.getmtime(image_path)
+            mtime_date = datetime.fromtimestamp(mtime).date()
+            return mtime_date
+    except Exception as e:
+        # Log error for debugging (but don't fail the import)
+        import logging
+        logger = logging.getLogger(__name__)
+        logger.debug(f"Failed to get file modification time from {image_path}: {e}")
+    
+    return None
+
+
 def find_photos_in_folder(folder_path: str, recursive: bool = True) -> list[str]:
     """Find all photo files in a folder."""
     folder_path = os.path.abspath(folder_path)
@@ -142,10 +172,17 @@ def import_photo_from_path(
     # Check if photo already exists by path
     existing = db.query(Photo).filter(Photo.path == photo_path).first()
     if existing:
+        # If existing photo doesn't have date_taken, try to update it
+        if existing.date_taken is None:
+            date_taken = extract_photo_date(photo_path)
+            if date_taken:
+                existing.date_taken = date_taken
+                db.commit()
+                db.refresh(existing)
         return existing, False
 
-    # Extract date taken (returns Date to match desktop schema)
-    date_taken = extract_exif_date(photo_path)
+    # Extract date taken with fallback to file modification time
+    date_taken = extract_photo_date(photo_path)
 
     # Create new photo record - match desktop schema exactly
     # Desktop schema: id, path, filename, date_added, date_taken (DATE), processed