---
fixes:
  - |
    Ensure request header keys are unique in link_content to prevent 400 Bad Request errors.

    Some image providers return a 400 Bad Request when using ImageContent.from_url() because the User-Agent
    header appears multiple times with different casing (e.g., user-agent, User-Agent).
    This update normalizes header keys in a case-insensitive way, removes duplicates, and
    preserves only the last occurrence.
