chore: add repo essentials and GitHub templates

- Add MIT LICENSE file
- Add CONTRIBUTING.md with skill creation guide
- Add AGENTS.md and CLAUDE.md for AI agent guidelines
- Add issue template for skill requests
- Add PR templates for new skills, updates, and docs
- Update README with links to contributing guide and license

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Agent Skills Specification
+    url: https://agentskills.io/specification.md
+    about: Learn the skill format before creating or requesting a skill
+  - name: Contributing Guide
+    url: https://github.com/coreyhaines31/marketingskills/blob/main/CONTRIBUTING.md
+    about: How to contribute a new skill to this repository