Centralize CORS configuration

Consolidate CORS handling by introducing a shared supabase/functions/_shared/cors.ts and migrate edge functions to import from it. Remove inline cors.ts usage across functions, standardize headers (including traceparent and x-request-id), and prepare for environment-aware origins.

supabase/functions/receive-inbound-email/index.ts

@@ -1,14 +1,10 @@
 import { serve } from "https://deno.land/std@0.190.0/http/server.ts";
 import { createClient } from "https://esm.sh/@supabase/supabase-js@2.57.4";
+import { corsHeaders } from '../_shared/cors.ts';
 import { edgeLogger, startRequest, endRequest } from "../_shared/logger.ts";
 import { createErrorResponse } from "../_shared/errorSanitizer.ts";
 import { formatEdgeError } from "../_shared/errorFormatter.ts";
 
-const corsHeaders = {
-  'Access-Control-Allow-Origin': '*',
-  'Access-Control-Allow-Headers': 'authorization, x-client-info, apikey, content-type',
-};
-
 interface InboundEmailPayload {
   from: string;
   to: string;