Add Copilot skill for new post prompt

Author: harrybin

.github/skills/create-new-post/SKILL.md

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+---
+name: create-new-post
+description: Turn the new post prompt into a reusable Copilot skill that creates a complete blog post from proposed content.
+---
+
+# Create New Post
+
+Create a new blog post from the proposed content in context.
+
+## Workflow
+
+1. Read the proposed content describing the topic.
+2. Do focused web research to validate and enrich important claims.
+3. Create the blog post markdown file in `src/content/blog/`.
+
+## Content requirements
+
+1. Add all required frontmatter fields for the blog collection.
+2. Improve, complete, and structure the content for readability and flow.
+3. Translate any German sentences to English.
+4. Rephrase awkward wording.
+5. Add missing but relevant context based on research.
+6. Add anything else needed for a complete, publishable post.
+
+## Style rules
+
+1. Do not use dashes for sentence parts.
+2. Do not put colons before an "and".
+
+## Project conventions
+
+1. Follow instructions in `.github/copilot-instructions.md`.
+2. Follow markdown rules in `.github/instructions/content-md.instructions.md`.
+3. Use `author: Harald Binkle`.
+4. Keep `description` in the 150 to 160 character range.
+5. Use a kebab-case filename unless `postSlug` requires a custom slug.
+6. Place blog posts only under `src/content/blog/`.
+
+## Output
+
+1. Create or update the target markdown file.
+2. Provide a short summary of what was added or improved.