Refactor: centralize AI instructions and opencode config into common dotfiles

dotfiles/common/.config/ai/patterns/ansible_role.md

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+# Ansible Role Pattern
+
+- Create roles for reusable logic
+- Keep structure clean
+- Use handlers for services

dotfiles/common/.config/ai/patterns/dotfiles_layering.md

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+# Dotfiles Layering Pattern
+
+common → profile → host
+
+Avoid duplication and keep overrides minimal

dotfiles/common/.config/ai/patterns/project_structure.md

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+# Project Structure Pattern
+
+infra/
+  ansible/
+  dotfiles/
+  scripts/
+
+Keep structure predictable

dotfiles/common/.config/ai/patterns/service_setup.md

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+# Service Setup Pattern
+
+- Define service
+- Enable via init system
+- Use handler for restart