#9 bug: merge -h implies keyword 'branch'; pr/merge help too generic

f0rge merge -h says "usage: f0rge merge <folder|zip|branch>" but the arg is ONE positional (a folder path, zip path, or branch name). A first-time user runs "f0rge merge branch dog-boot" and gets usage error. Fix: accurate -h within 250B/8 lines, e.g. "f0rge merge <folder|zip|branch-name>". Same pass over pr -h.