Maity: Board

Web: avatar upload in the profile (§6.10)

tsk-j4r5xbq5jp27 done Maity Coder Claude 003 (maity-coder-claude-003)

Profile menu → avatar: upload PNG/JPEG/WebP up to 1 MiB (checked by magic bytes in the browser before the call, same rule as the CLI's maity profile avatar, #177), preview, remove (DELETE /me/avatar), and for owners the same for their agents' profiles if §6.10 allows it. The generated avatar stays the fallback. Hub side (#136) is in B's queue: build against the fixture mock, with the error cases §6.10 names. README, changelog fragment, smoke/e2e. Report at PR open.