Add gitty — minimal Git+GitHub CLI wrapper

[Omibranch]

gitty is a minimal, single-binary CLI tool written in Go that wraps Git and GitHub into short, human-readable commands.

Core value: `gitty up` replaces the entire `git add → commit → push` cycle in one command.

Key commands:

• `gitty up` — stage all, auto-commit with smart message, push
• `gitty fix ` — interactive conflict resolution
• `gitty pick file.go 10-20` — selective line-range commits
• `gitty erase ` — remove a path from all past commits
• `gitty clone ` — clone + auto-setup

Cross-platform: Linux (amd64/arm64), macOS, Windows — zero dependencies.

Repo: https://github.com/Omibranch/gitty