fix(data-store-form): add change detection, fix button class, restore textarea height

- Add original_obj prop + has_changes bindable output to element_data_store_form
- Derive has_changes by comparing each draft field to original_obj; null = always dirty (new record)
- Wire bind:has_changes + original_obj={is_new ? null : editing_obj} in management page
- Fix Save button: preset-filled-primary → preset-filled-primary-500 (matches element_data_store)
- Disable Save when !has_changes; block modal outsideclose when changes are pending
- Restore textarea rows 10 → 15 to match element_data_store.svelte

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/core/data_stores/+page.svelte

@@ -71,6 +71,7 @@ let draft_sort = $state('');
 let draft_group = $state('');
 let draft_notes = $state('');
 let submit_status = $state<'idle' | 'processing' | 'saved' | 'error'>('idle');
+let has_changes = $state(false); // bound from form component — true when any draft differs from editing_obj
 
 // ── Bulk rename state ─────────────────────────────────────────────────────────
 let show_bulk_rename = $state(false);
@@ -734,7 +735,7 @@ function content_preview(ds: ae_DataStore): string {
     title={is_new ? 'New Data Store' : `Edit: ${editing_obj?.code ?? ''}`}
     bind:open={show_edit}
     autoclose={false}
-    outsideclose={submit_status !== 'processing'}
+    outsideclose={!has_changes}
     size="xl"
     class="w-full max-w-5xl">
 
@@ -758,7 +759,9 @@ function content_preview(ds: ae_DataStore): string {
                 bind:draft_sort
                 bind:draft_group
                 bind:draft_notes
-                {is_new} />
+                {is_new}
+                original_obj={is_new ? null : editing_obj}
+                bind:has_changes />
         {/key}
 
         <!-- Footer actions -->
@@ -785,8 +788,8 @@ function content_preview(ds: ae_DataStore): string {
                 </button>
                 <button
                     type="submit"
-                    class="btn preset-filled-primary"
-                    disabled={submit_status === 'processing'}
+                    class="btn preset-filled-primary-500"
+                    disabled={!has_changes || submit_status === 'processing'}
                     title={is_new ? 'Create new data store' : 'Save changes'}>
                     {#if submit_status === 'processing'}
                         <LoaderCircle size={14} class="mr-2 animate-spin" />