feat: introduce new skills and refine existing ones

- Add `ask-matt` skill for user-invoked routing.
- Introduce `codebase-design` and `domain-modeling` skills, updating dependencies.
- Remove unused `caveman` and `zoom-out` skills.
- Rename `diagnose` skill to `diagnosing-bugs`.
- Add `resolving-merge-conflicts` skill for handling git conflicts.
- Tighten `review` skill with improved checks.
- Update skill taxonomy to user-invoked and model-invoked.
- Replace `write-a-skill` with `writing-great-skills` for better guidance.

.changeset/remove-caveman-and-zoom-out.md

@@ -0,0 +1,10 @@
+---
+"mattpocock-skills": major
+---
+
+Remove the **`caveman`** and **`zoom-out`** skills.
+
+- `caveman` was a duplicate of another skill I was testing and was never meant to be public.
+- `zoom-out` went unused in practice, so it's been removed from the repo.
+
+**Breaking:** both skills have been removed.