feat: major dotfiles refactor with documentation and multi-platform improvements

- Add comprehensive CLAUDE.md with chezmoi best practices and AI assistant guidelines
- Restructure TODO.md with prioritized tasks and detailed organization
- Add PowerShell profile template for Windows platform support
- Split git configs into identity-specific templates (ryan/xevion)
- Convert nushell env.nu and gitconfig to templates for cross-platform rendering
- Refactor chezmoi hooks to TypeScript (.init_pre.ts, .update_pre.ts)
- Update .chezmoiignore with better platform-specific file handling
- Remove deprecated shellchecker.sh and tasks.json from VS Code config
- Add mise integration to shell configs (bash, zsh, nushell, PowerShell)
- Clean up commonrc.sh.tmpl WSL-specific code
- Disable Deno in VS Code settings, enable simple dialog mode
- Add nushell extension recommendation to VS Code

This commit establishes better cross-platform support (Windows/WSL/Linux),
improves documentation for future maintenance, and standardizes configuration
management patterns across the repository.

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+    "recommendations": [
+        "thenuprojectcontributors.vscode-nushell-lang"
+    ]
+}