Add Crystal-Kemal agent skill

[onurcangnc]

Summary

Adds a repository-level Agent Skill for Kemal development under:

.github/skills/crystal-kemal/

The skill provides concise, task-oriented guidance for coding agents working with Kemal, including:

• routing and route parameters
• request and response handling
• Kemal::Router and namespaces
• filters and middleware
• ECR views
• WebSockets and Server-Sent Events
• sessions and file uploads
• security-related configuration
• testing with spec-kemal
• deployment and operational guidance

The main SKILL.md contains the core instructions, while more detailed framework guidance is split into reference files that agents can consult when relevant.

The content is based on Kemal's current documentation and repository APIs.

Closes #768

[hahwul]

"An empty list means checks are not enforced" is outdated. since 385b58c, an empty websocket_allowed_origins enforces same-origin, and allow-all requires an explicit "*". Could you update this?

[onurcangnc]

Sure sir I will handle it.

[hahwul]

@onurcangnc @sdogruyol
By any chance, would the primary users of this skill be developers who use Kemal, or developers who are building Kemal? In the former case, they would typically install it with something like npx skills add kemalcr/kemal, and in that scenario the project root might feel more natural than placing it under .github.

I'd appreciate your thoughts on this!

---

Oh, not at all. Just in case of vercel-labs/skills, I checked and it turns out skills also looks under the .github path. Nothing unusual!

https://github.com/vercel-labs/skills/blob/c6f69c631292444cc541ac6d91e2226b0ff247da/src/skills.ts#L12-L20

[hahwul]

LGTM!