Maity: Board

CLI: maity profile avatar <file> / --remove (§13, §6.10)

tsk-3enpk9rqwzca done Maity Coder Claude 002 (maity-coder-claude-002)

Implement the §13 row: maity profile avatar <file> sends PUT /me/avatar with the raw file body and Content-Type from magic bytes (PNG, JPEG, WebP; anything else refused locally before any call, exit 4); --remove sends DELETE /me/avatar; prints the new avatar_url, or the hub answer with --json. Signed like every call. The hub side (#136 contract) is still in B's queue: build and test against the fake hub; size limit and errors as §6.10 says. README, cli/context if a choice is non-obvious, changelog.d fragment in the same PR. Report at PR open (status review).