Simplify dotfile utilities

[lcmen]

Summary

• remove the unused gw worktree helper and its Fish completion
• rename rp to photon and fix counter increments that aborted under set -e
• extract stale-branch cleanup into the executable git-fe command
• add lightweight CI for Bash, Fish, PowerShell, TOML, and whitespace validation
• document photon usage

Why

The worktree helper is no longer needed, while the photo renamer could exit after its first processed file because Bash post-increment returns a failing status when incrementing from zero under set -e. Extracting git-fe also keeps the Git configuration simple and makes the behavior easier to maintain.

Validation

• git diff --check --cached
• Bash syntax checks
• Fish syntax checks
• workflow YAML parsing
• TOML parsing
• manual git-fe verification for no-op and stale-upstream cases