feat(pres_mgmt): make session code editable in edit mode

The code badge was display-only — replaced with a field editor so staff
can correct session codes without going to a separate admin view.

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

src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/session_view.svelte

@@ -172,8 +172,22 @@ $effect(() => {
                     {/if}
 
                     {#if $ae_loc.edit_mode}
-                        <span class="badge preset-tonal-surface mt-1 text-xs"
-                            >code: {$lq__event_session_obj.code}</span>
+                        <Element_ae_obj_field_editor
+                            object_type="event_session"
+                            object_id={$lq__event_session_obj.id}
+                            field_name="code"
+                            field_type="text"
+                            edit_label="Session Code"
+                            current_value={$lq__event_session_obj.code}
+                            placeholder="e.g. SES-101"
+                            on_success={() =>
+                                events_func.load_ae_obj_id__event_session({
+                                    api_cfg: $ae_api,
+                                    event_session_id: $lq__event_session_obj.id
+                                })}>
+                            <span class="badge preset-tonal-surface mt-1 text-xs"
+                                >code: {$lq__event_session_obj.code}</span>
+                        </Element_ae_obj_field_editor>
                     {/if}
                 </div>
             {:else}