Migrate frontend to Svelte 5 runes semantics

frontend/src/routes/migration/mappings/+page.svelte

@@ -181,19 +181,19 @@
         label={$t.migration?.source_env }
         bind:selectedId={sourceEnvId}
         {environments}
-        on:change={() => { sourceDatabases = []; mappings = []; suggestions = []; }}
+        onchange={() => { sourceDatabases = []; mappings = []; suggestions = []; }}
       />
       <EnvSelector
         label={$t.migration?.target_env }
         bind:selectedId={targetEnvId}
         {environments}
-        on:change={() => { targetDatabases = []; mappings = []; suggestions = []; }}
+        onchange={() => { targetDatabases = []; mappings = []; suggestions = []; }}
       />
     </div>
 
     <div class="mb-8">
       <Button
-        on:click={fetchDatabases}
+        onclick={fetchDatabases}
         disabled={!sourceEnvId || !targetEnvId || sourceEnvId === targetEnvId || fetchingDbs}
         isLoading={fetchingDbs}
       >
@@ -219,7 +219,7 @@
         {targetDatabases}
         {mappings}
         {suggestions}
-        on:update={handleUpdate}
+        onupdate={handleUpdate}
       />
     {:else if !fetchingDbs && sourceEnvId && targetEnvId}
       <p class="text-gray-500 italic">{$t.migration?.mapping_hint }</p>