fix: drop avatarUrl from Maple webhook create payload (#318)

The channelWebhook.create RPC validates avatarUrl by HEAD-fetching the URL
and asserting Content-Type starts with image/. Brandfetch's CDN now serves
a 302 redirect to its hotlinking guidelines (text/html) on direct hits, so
passing the Brandfetch icon URL fails validation:

  defect: "Avatar URL must point to an image\n  at [\"avatarUrl\"]"

The webhook record's avatarUrl is only used as a fallback in the channel
integrations settings list. The bot identity that actually appears on
posted messages is resolved via WEBHOOK_BOT_CONFIGS.maple by
IntegrationBotService.getOrCreateWebhookBotUser, which is unaffected by
the create payload. Dropping the field unblocks creation without changing
the rendered embed.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Makisuo

apps/web/src/components/channel-settings/maple-section.tsx

@@ -64,7 +64,6 @@ export function MapleSection({
 				channelId,
 				name: MAPLE_NAME,
 				description: "Maple alert notifications",
-				avatarUrl: mapleLogoUrl,
 				integrationProvider: "maple",
 			},
 		})