feat: migrate from Zsh to Fish shell with comprehensive configuration

Major shell migration replacing Zsh/Oh-My-Zsh with Fish shell:

- Remove all Zsh configurations (dot_zshrc.tmpl, dot_p10k.zsh)
- Remove Oh-My-Zsh external dependencies from .chezmoiexternal.toml
- Add complete Fish shell setup with config.fish.tmpl and abbr.fish.tmpl
- Implement Fish-native functions for lazy-loading tools (mise, pyenv, zoxide, etc.)
- Create commonrc.fish.tmpl for cross-shell compatibility
- Add Fish plugin management via Fisher (tide prompt, fzf.fish)
- Update documentation (CLAUDE.md, TODO.md, ONBOARDING.md) to reflect Fish
- Add .fish.tmpl file association to VS Code settings
- Enhance PowerShell profile with lsd aliases
- Configure git delta pager and zdiff3 merge conflict style
- Update WSL keychain integration for Fish shell

This migration maintains all existing tool integrations while improving
startup performance through lazy-loading and Fish's native features.

home/dot_config/fish/functions/chfix.fish

@@ -0,0 +1,12 @@
+function chfix --description "chmod +x the last command (if it's a file)"
+    # Get the last command from Fish history
+    set -l last_command (history --max 1 | string trim)
+
+    if test -f "$last_command"
+        chmod +x "$last_command"
+        echo "Made executable: $last_command"
+    else
+        echo "Error: $last_command is not a valid file"
+        return 1
+    end
+end