Add gallery date jump navigation

[Kaed3mi]

Summary

This PR adds date-based jump navigation for gallery list pages, matching the E-Hentai seek/jump behavior available at the bottom of the website.

The feature is currently enabled for:

• Frontpage
• Search results

Changes

• Parse gallery list jump metadata from page scripts:
  • prevurl
  • nexturl
  • mindate
  • maxdate
• Extend pagination state with optional jump navigation metadata.
• Add a JumpGalleriesRequest that loads galleries from a generated seek URL.
• Add a toolbar date jump button for Frontpage and Search.
• Show a date picker and jump toward newer or older results depending on the available navigation direction.
• Replace the current gallery list and pagination state after a successful jump.
• Add parser / URL tests for the new jump navigation behavior.

Testing

• Added unit coverage for parsing jump navigation metadata.
• Added coverage for generating seek=YYYY-MM-DD jump URLs.