Add Broad Site Icon Fetcher extension

[bowencool]

Summary

• Register bowencool/xExtension-BroadIconFetcher as a third-party extension repository.
• Add the extension to the community list in the README.

Why

Broad Site Icon Fetcher expands FreshRSS favicon discovery by preferring RSS/Atom channel images, then checking web manifests, metadata, and standard HTML favicon declarations.

User impact

The repository will be discovered by the generated extension list and can be installed by tools that consume the FreshRSS community repository catalogue.

Validation

• Confirmed repositories.json is valid JSON.
• Confirmed the public repository exposes complete metadata.json with version 0.1.2.
• Tested RSS/Atom channel-image extraction against an RSSHub feed.

[bowencool]

Sorry for the delay—I was fixing a bug during these hours. It works well now.

[Alkarex]

Hello!
For reference, the latest changes in core:

• feat(favicon): Use feed-provided icon URL (<image><url>, Atom icon/logo, JSON Feed icon) FreshRSS#8633

If there are some standard improvements in this extension (so not specific to e.g. YouTube), it could be an idea to promote them to the core.