Feat: Add a Dev Portal agent skill

Create a Dev Portal "product specific" skill which will aide a user in creating new or managing existing dev portals. Here are some sample goals described via prompts:

- Create a new Kong Konnect developer portal from the openapi spec in this repository. Use the brand assets located in the `@branding/` folder and follow the general style of our home page https://ourcompany.com
- Generate declarative configuration files from our current konnect dev portal named "platform team portal" and help me create github actions to manage them in CICD
- Add the new `@apis/spec-123.json` to our konnect dev portal declarative configuration in this project
- Add the new `@apis/spec-123.json` to our konnect dev portal and add a documentation page like the others in the `@konnect/apis` folder

Build the skill and validate some initial results via popular coding tools.

Start by examining the existing project structure around @branding/, @apis/spec-123.json, and @konnect/apis to understand the assets and declarative configuration referenced in the goals. Then determine the skill entry point and how it should be validated with popular coding tools; done means the skill supports the described portal-management prompts and produces useful initial results.

Written by the indexing model from the issue text.