feat: add channel/type icons to session list in sidebar

Show Discord, Telegram, WhatsApp, Signal, Slack brand icons,
clock icon for cron sessions, bot icon for sub-agents, and
globe icon for webchat sessions. Falls back to message bubble
for unknown channels.

Closes feedback #23

src/hooks/useGateway.ts

@@ -90,6 +90,8 @@ export function useGateway() {
           contextTokens: s.contextTokens as number | undefined,
           inputTokens: s.inputTokens as number | undefined,
           outputTokens: s.outputTokens as number | undefined,
+          channel: (s.lastChannel || s.channel) as string | undefined,
+          kind: s.kind as string | undefined,
         })));
       }
     } catch {