Consumes the GET /icon endpoint from #139:
- Dashboard: each container card shows the agent's icon next to its
name (26px). Loaded from <agent-url>/icon; onerror hides it for a
stopped container whose web server isn't answering.
- Per-agent web UI: the agent's icon next to the page title (40px),
and /icon as the favicon on the index, stats, and screen pages.
/icon always returns an image (configured SVG or the default
hyperhive logo), so no presence check is needed.
Closes#140
62aa3bb3ec