Migrate frontend to Svelte 5 runes semantics

frontend/src/components/EnvSelector.svelte

@@ -10,7 +10,6 @@
 
 <script lang="ts">
   // [SECTION: IMPORTS]
-  import { onMount, createEventDispatcher } from 'svelte';
   import { t } from '../lib/i18n';
   // [/SECTION]
 
@@ -19,23 +18,22 @@
     label = "",
     selectedId = "",
     environments = [],
+    onchange = () => {},
   } = $props();
 
   // [/SECTION]
 
-  const dispatch = createEventDispatcher();
-
   // [DEF:handleSelect:Function]
   /**
-   * @purpose Dispatches the selection change event.
+   * @purpose Propagates the selection change through a callback prop.
    * @pre     event.target must be an HTMLSelectElement.
-   * @post    selectedId is updated and 'change' event is dispatched.
+   * @post    selectedId is updated and parent callback receives the selected environment id.
    * @param   {Event} event - The change event from the select element.
    */
   function handleSelect(event: Event) {
     const target = event.target as HTMLSelectElement;
     selectedId = target.value;
-    dispatch('change', { id: selectedId });
+    onchange({ id: selectedId });
   }
   // [/DEF:handleSelect:Function]
 </script>
@@ -47,7 +45,7 @@
     id="env-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={selectedId}
-    on:change={handleSelect}
+    onchange={handleSelect}
   >
     <option value="" disabled>{$t.common?.choose_environment}</option>
     {#each environments as env}