Initial shared Copilot resources scaffold

resources/skills/resource-authoring/SKILL.md

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+---
+name: resource-authoring
+description: "Use when adding, publishing, or reviewing shared Copilot resources such as skills, prompts, instructions, agents, hooks, or supporting scripts."
+argument-hint: "[resource type] [goal]"
+---
+
+# Resource Authoring
+
+Use this skill when the task is to create or evolve a shared Copilot resource in
+the repository.
+
+## Procedure
+
+1. Decide whether the resource should be a skill, prompt, agent, instruction,
+   or hook.
+2. Prefer repo-first authoring when the work is intentionally shared.
+3. If the resource originated elsewhere, publish it into the repository.
+4. Review naming, portability, and lifecycle impact.
+5. Validate any scripts or automation referenced by the resource.
+
+## References
+
+- [Publishing checklist](./references/publishing-checklist.md)