v0.2.1 — fix CoS dashboard onboarding + per-agent bot avatars

Fixes the 0.2.0 CoS dashboard onboarding (it never rendered) + adds per-agent bot avatars

Bugfix (DIVE-320): In 0.2.0 the new-agent wizard's "Create a bot automatically" path never appeared — it silently fell back to pasting a token. agent cos verify/mint-link emitted a bare {ok:true,username,...} JSON, but the dashboard unwraps the standard {ok:true,data:{...}} envelope, so the result read as empty and the probe failed. Both subcommands now return the standard envelope. (claim/rotate stay bare — they're consumed by the create-path, not the dashboard.)

Feature (DIVE-325): 5dive agent cos set-avatar --agent=<name> --avatar=<png> sets an existing agent's Telegram bot profile photo (works for any telegram agent). Surfaced in the dashboard as a per-agent "Bot avatar" upload in the agent settings tab.

Managed boxes pick this up on the nightly refresh; self-hosted: 5dive self-update. The dashboard half ships via the web app. Note: the dashboard CoS onboarding + avatar upload require the box CLI to be >= 0.2.1.