Add Makefile with install/uninstall for the clone-based workflow

`make install` symlinks f5-connect into ~/.local/bin (BINDIR override
supported) and seeds ~/.config/f5-connect/config on first run; the clone
stays the source of truth (git pull to update). `make uninstall` removes
the symlink and leaves the config in place. README documents it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>