refactor(pres_mgmt): consistent layout, menu structure, and centering

- Add (pres_mgmt)/+layout.svelte with shared section wrapper (max-w-7xl mx-auto)
  so all child pages center correctly on wide viewports
- Strip per-page outer <section> tags from session, presenter, location pages;
  replace with inner <div max-w-7xl mx-auto> for detail constraint
- Restructure all page menus from flex-row to flex-col so nav bar occupies its
  own row and options/actions sit in a separate justified row below — prevents
  unwanted wrapping when nav is w-full
- Standardize Æ Core button visibility to edit_mode && manager_access across all
  menus; update button style to ae_btn_warning for visual distinction
- Add w-full + justify-between to ae_comp__events_menu_nav outer div

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

src/routes/events/ae_comp__events_menu_nav.svelte

@@ -46,7 +46,7 @@
 
 <!-- This is for common navigation links. -->
 <div
-    class="ae_comp__events_menu_nav flex flex-row flex-wrap gap-1.5 items-center justify-around"
+    class="ae_comp__events_menu_nav w-full flex flex-row flex-wrap gap-1.5 items-center justify-between"
     class:hidden={hide}
 >
     <span
@@ -54,7 +54,7 @@
     >
         <a
             href="/core"
-            class="btn btn-sm mx-1 ae_btn_info"
+            class="btn btn-sm mx-1 ae_btn_warning"
             class:hidden={!ae_core}
         >
             <span class="fas fa-cogs m-1"></span>