Add new skills for TDD, issue management, PRD creation, and productivity tools

- Introduced TDD skills including deep modules, interface design, mocking, refactoring, and testing guidelines.
- Added skills for breaking plans into GitHub issues and creating PRDs from conversation context.
- Implemented productivity skills for scaffolding exercises, setting up pre-commit hooks, and managing notes in Obsidian.
- Created a caveman communication mode for concise technical responses and a grilling technique for thorough plan discussions.
- Developed a skill for writing new agent skills with structured templates and guidelines.
- Included git guardrails to prevent dangerous git commands and a migration guide for using @total-typescript/shoehorn in tests.

skills/deprecated/README.md

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+# Deprecated
+
+Skills I no longer use.

skills/engineering/README.md

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+# Engineering
+
+Skills I use daily for code work.

skills/misc/README.md

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+# Misc
+
+Tools I keep around but rarely use.

skills/personal/README.md

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+# Personal
+
+Skills tied to my own setup, not promoted in the plugin.

skills/productivity/README.md

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+# Productivity
+
+General workflow tools, not code-specific.