fix: normalize platform ID at registration, not router lookup

Channel adapters prefix platform IDs with their channel type
(e.g. "telegram:123"). Normalize in register.ts so the DB always
stores the canonical format. Removes fallback lookup from router.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/router.ts

@@ -34,15 +34,7 @@ export interface InboundEvent {
  */
 export async function routeInbound(event: InboundEvent): Promise<void> {
   // 1. Resolve messaging group
-  // Adapters send prefixed platform IDs (e.g. "telegram:123") but users may
-  // register with raw IDs ("123"). Try exact match first, then stripped prefix.
   let mg = getMessagingGroupByPlatform(event.channelType, event.platformId);
-  if (!mg) {
-    const prefix = `${event.channelType}:`;
-    if (event.platformId.startsWith(prefix)) {
-      mg = getMessagingGroupByPlatform(event.channelType, event.platformId.slice(prefix.length));
-    }
-  }
 
   if (!mg) {
     // Auto-create messaging group (adapter already decided to forward this)