Make gallery page fully mobile responsive

GalleryLayout improvements:
- Stack header elements vertically on mobile
- Hide company branding on small screens
- Make dates stack vertically
- Responsive text sizes and padding
- Icon-only logout button on mobile
- Improved button layout with proper wrapping

PhotoFilterBar improvements:
- Stack search and sort vertically on mobile
- Full-width sort button on mobile
- Horizontally scrollable category filters
- Responsive text sizes
- Mobile-friendly dropdown positioning

PhotoGrid improvements:
- Responsive selection controls
- Touch-friendly photo overlays
- Larger selection checkboxes on mobile
- Improved button text for small screens
- Responsive gaps between photos

Gallery grid CSS:
- Smaller gaps on mobile devices
- Maintains 2 columns on smallest screens

GalleryPage login:
- Responsive padding and margins
- Smaller text and icon sizes on mobile
- Better card spacing
- Responsive form elements

UserPhotoUpload modal:
- Full-screen modal on mobile (slides up from bottom)
- Responsive padding and text sizes
- Mobile-optimized upload area
- Sticky footer on mobile

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

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

frontend/src/components/gallery/GalleryView.tsx

@@ -236,9 +236,10 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
               size="md"
               leftIcon={<Upload className="w-4 h-4" />}
               onClick={() => setShowUploadModal(true)}
-              className="mr-2"
+              className="mr-2 text-sm sm:text-base"
             >
-              {t('upload.uploadPhotos')}
+              <span className="hidden sm:inline">{t('upload.uploadPhotos')}</span>
+              <span className="sm:hidden">{t('common.upload')}</span>
             </Button>
           )}
         </>