Fix: Add embed title URL input and preview link - #143

Description

Adds a new "Title URL" field to embed editors in the tag modal and KB create/edit pages, wired to embed.url with existing URL length limits. Embed previews now render the title as a clickable link (with Discord-like link styling) when a safe URL is provided, while preserving the plain title fallback when no valid URL exists.

Type of Change

• Bug fix
• New feature
• Breaking change

Checklist

• My code follows the style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works