offline: Nginx start fail issues & local images route & enlarge images

[haolloyin]

1. Fixed an issue where Nginx failed to start when the offline release package
   was extracted to a directory with spaces in its absolute
   path (e.g., Program Files in Windows).

Enclose path-related configurations in nginx.conf within double quotes.

[haolloyin]

2. Use Nginx to route local image paths from frontend/dist/img/arkham to the
   directory where start.sh is located, making it easier for offline package users
   to place high-resolution placeholder images.

Nginx request processing chain:

Request for /img/arkham/cards/01104.avif (English)
→ 1. alias cards/en/ → Look for cards/en/01104.avif
→ 2. @img_builtin → Look for frontend/dist/img/arkham/cards/01104.avif
→ 3. @img_cdn → Fetch from CDN origin

Request for /img/arkham/zh/cards/01104.avif (Chinese)
→ 1. alias cards/zh/ → Look for cards/zh/01104.avif
→ 2. @img_builtin → Look for frontend/dist/img/arkham/zh/cards/01104.avif
→ 3. @img_cdn → Fallback to CDN origin

Users simply need to place card images in the top-level
cards/en/ or cards/zh/ directories; existing files
in frontend/dist/ remain untouched as a fallback.

[haolloyin]

3. By default, images from the official CDN do not display a hint icon
   in the upper-right corner, unless the user selects this option on the settings page.

Reason: Clicking the icon allows users to jump directly to the corresponding
page on arkhamdb.com to view card details.

[haolloyin]

4. Users can select a +N% scaling factor in the settings page to proportionally
   enlarge in-game hover images.

Reason: Users of the offline package feel that local high-resolution images
should be enlarged for better visibility, especially since they have larger
screens and the hover images in the original repository are currently quite small.

Note: Both of the above features currently apply only to the offline version;
they do not modify the original repository’s source code but are implemented through
modifications or injections during compilation.

Hi @halogenandtoast, do you think the original repo needs the image zoom feature?
I can modify the source code and submit a PR.