[Feature] Expand the extension marketplace to support more extensions

[RA1NCS]

Feature summary

Athas currently has a limited set of extensions available. Since it shares architectural DNA with Zed's extension model (Tree-sitter grammars, LSP configs), there's an opportunity to expand compatibility with the broader Zed extension ecosystem rather than requiring everything to be purpose-built for Athas.

Requested behavior

• Broaden the extension registry to include languages, themes, and LSP configs already available in the Zed extension ecosystem where they're compatible
• Ideally, allow installing Zed-compatible extensions directly, or provide a compatibility layer / import path for them
• At minimum, expose the extension API surface clearly so the community can port extensions faster

Why this matters

Right now, the extension library is thin. Language support gaps and missing themes are frequently a blocker for new users trying to adopt Athas as a daily driver. Bootstrapping off the Zed extension ecosystem would massively accelerate this without requiring everything to be rebuilt from scratch.

What would help from the maintainers

• Clarification on how much of Zed's extension format is currently compatible with Athas
• A guide or template for porting Zed extensions
• Visibility into which extension categories are highest priority for official support (language grammars, themes, LSP wrappers, etc.)