fix(field-editor-v3): layout shift, bindable crash, and optimistic display

- Fix layout shift on edit_mode toggle: always render the edit button
  (using invisible/pointer-events-none) so the flex container doesn't
  reflow when edit_mode is toggled on/off.

- Fix 'store.set is not a function' crash: remove $bindable() from
  current_value. The component is SWR-first; after a successful PATCH
  liveQuery updates the prop from Dexie. Trying to write back to a
  readonly liveQuery-derived prop caused the crash.

- Fix stale display after save: add has_optimistic flag + display_value
  derived. After a successful PATCH, display_value shows draft_value
  immediately without waiting for liveQuery. Cleared automatically when
  current_value catches up, or on cancel/re-open of edit mode.

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

src/lib/elements/element_ae_obj_field_editor_v3.svelte

@@ -47,7 +47,7 @@
         object_type,
         object_id,
         field_name,
-        current_value = $bindable(),
+        current_value,
         field_type = 'text',
         allow_null = false,
         select_options = {},
@@ -70,15 +70,31 @@
     let error_message = $state('');
     let draft_value = $state(current_value);
 
-    // Sync draft with current_value when not editing
+    // WHY: Optimistic display. After a successful PATCH, liveQuery may not fire
+    // immediately (or at all if on_success doesn't trigger a Dexie refresh). We show
+    // draft_value as the display until current_value catches up from liveQuery.
+    let has_optimistic = $state(false);
+    let display_value = $derived(has_optimistic ? draft_value : current_value);
+
+    // Sync draft with display_value when not editing.
+    // Suppress reset if optimistic is active — we already have the right value.
     $effect(() => {
         if (!is_editing) {
             untrack(() => {
-                draft_value = current_value;
+                if (!has_optimistic) {
+                    draft_value = current_value;
+                }
             });
         }
     });
 
+    // Clear optimistic once liveQuery catches up (current_value matches what we saved)
+    $effect(() => {
+        if (has_optimistic && current_value === draft_value) {
+            has_optimistic = false;
+        }
+    });
+
     async function handle_patch() {
         if (log_lvl) console.log(`AE Field Editor V3: Patching ${object_type}.${field_name}...`);
 
@@ -98,7 +114,7 @@
 
             if (result) {
                 patch_status = 'success';
-                current_value = draft_value;
+                has_optimistic = true; // show draft_value immediately; cleared when liveQuery catches up
                 if (on_success) on_success(result);
 
                 // Close edit mode after a brief success indicator
@@ -120,6 +136,7 @@
     }
 
     function cancel_edit() {
+        has_optimistic = false;
         draft_value = current_value;
         is_editing = false;
         patch_status = 'idle';
@@ -128,7 +145,11 @@
 
     function toggle_edit() {
         if (is_editing) cancel_edit();
-        else is_editing = true;
+        else {
+            has_optimistic = false; // clear optimistic so draft syncs from current prop
+            draft_value = current_value;
+            is_editing = true;
+        }
     }
 </script>
 
@@ -143,31 +164,33 @@
             {#if children}
                 {@render children()}
             {:else if field_type === 'checkbox'}
-                <span class="badge {current_value ? 'variant-filled-success' : 'variant-soft-surface'}">
-                    {current_value ? 'Enabled' : 'Disabled'}
+                <span class="badge {display_value ? 'variant-filled-success' : 'variant-soft-surface'}">
+                    {display_value ? 'Enabled' : 'Disabled'}
                 </span>
             {:else if field_type === 'tiptap'}
                 <div class="prose dark:prose-invert max-w-none">
-                    {@html current_value || '<span class="opacity-50 italic">Empty</span>'}
+                    {@html display_value || '<span class="opacity-50 italic">Empty</span>'}
                 </div>
             {:else}
-                <span class:opacity-50={!current_value}>
-                    {current_value || 'Not set'}
+                <span class:opacity-50={!display_value}>
+                    {display_value || 'Not set'}
                 </span>
             {/if}
         </div>
 
         <!-- Edit Trigger (Visible on Hover or Edit Mode) -->
-        {#if $ae_loc.edit_mode}
-            <button
-                type="button"
-                class="btn-icon btn-icon-sm variant-soft-warning opacity-0 group-hover:opacity-100 transition-opacity"
-                onclick={toggle_edit}
-                title="Edit {field_name}"
-            >
-                <SquarePen size="14" />
-            </button>
-        {/if}
+        <!-- WHY: Always render to avoid layout shift when edit_mode toggles.
+             Use invisible (visibility:hidden, preserves space) when edit_mode is off. -->
+        <button
+            type="button"
+            class="btn-icon btn-icon-sm variant-soft-warning opacity-0 group-hover:opacity-100 transition-opacity"
+            class:invisible={!$ae_loc.edit_mode}
+            class:pointer-events-none={!$ae_loc.edit_mode}
+            onclick={toggle_edit}
+            title="Edit {field_name}"
+        >
+            <SquarePen size="14" />
+        </button>
     </div>
 
     <!-- EDIT MODE -->
@@ -263,7 +286,7 @@
                         type="button"
                         class="btn btn-sm variant-filled-primary"
                         onclick={handle_patch}
-                        disabled={patch_status === 'processing' || draft_value === current_value}
+                        disabled={patch_status === 'processing' || draft_value === display_value}
                     >
                         {#if patch_status === 'processing'}
                             <LoaderCircle size="14" class="animate-spin mr-1" />