Migrate frontend to Svelte 5 runes semantics

frontend/src/components/MappingTable.svelte

@@ -10,7 +10,6 @@
 
 <script lang="ts">
   // [SECTION: IMPORTS]
-  import { createEventDispatcher } from 'svelte';
   import { t } from '$lib/i18n';
   // [/SECTION]
 
@@ -20,23 +19,22 @@
     targetDatabases = [],
     mappings = [],
     suggestions = [],
+    onupdate = () => {},
   } = $props();
 
   // [/SECTION]
 
-  const dispatch = createEventDispatcher();
-
   // [DEF:updateMapping:Function]
   /**
    * @purpose Updates a mapping for a specific source database.
    * @pre sourceUuid and targetUuid are provided.
-   * @post 'update' event is dispatched.
+   * @post Parent callback receives normalized mapping payload.
    */
   function updateMapping(sourceUuid: string, targetUuid: string) {
     const sDb = sourceDatabases.find(d => d.uuid === sourceUuid);
     const tDb = targetDatabases.find(d => d.uuid === targetUuid);
     
-    dispatch('update', { 
+    onupdate({ 
       sourceUuid, 
       targetUuid,
       sourceName: sDb?.database_name || "",
@@ -80,7 +78,7 @@
             <select
               class="block w-full pl-3 pr-10 py-2 text-base border-gray-300 focus:outline-none focus:ring-indigo-500 focus:border-indigo-500 sm:text-sm rounded-md"
               value={mapping?.target_db_uuid || suggestion?.target_db_uuid || ""}
-              on:change={(e) => updateMapping(sDb.uuid, (e.target as HTMLSelectElement).value)}
+              onchange={(e) => updateMapping(sDb.uuid, (e.target as HTMLSelectElement).value)}
             >
               <option value="">{$t.migration?.target_env }</option>
               {#each targetDatabases as tDb}