docs: add UI style guidelines + component patterns reference

- GUIDE__AE_UI_Style_Guidelines.md: overall design system
  - Firefly theme semantics (Primary/Secondary/Tertiary/Surface)
  - Forbidden class list (bg-gray-*, variant-soft-*, rounded-container-token, etc.)
  - Skeleton v3 -> v4 migration table
  - Transition, a11y, dark mode, QR type-guard rules
  - Debug code to remove checklist
- AE__UI_Component_Patterns.md: per-component class recipes
  - Hero card, standard card, table row, list item, info chips
  - Empty state, upload zone, section wrapper, agree forms
  - Modal, muted text, QR code, icon usage

pres_mgmt: complete styling cleanup (second pass)
- location/+page.svelte: rounded-container-token -> rounded-xl
- location_view.svelte: code chip yellow -> preset-tonal-warning;
  description pre bg-gray-100 -> bg-surface-100-900
- ae_comp__event_presenter_obj_li.svelte: remove debug borders,
  overflow-x-scroll -> overflow-x-auto, ul bg-gray-100 removed
- presenter/[presenter_id]/+page.svelte:
  - Both upload zones: bg-gray-100 -> surface tokens with transition
  - Label text: text-gray-600 dark:text-gray-400 -> opacity-60
  - Modal: remove bg-white dark:bg-gray-800 theme bypass
- pres_mgmt/+page.svelte: event upload zone same surface token fix
- ae_comp__event_session_poc_form_agree.svelte:
  - bg-gray-100 container -> bg-surface-100-900
  - bg-yellow-100 identity line -> preset-tonal-warning
- ae_comp__event_presenter_form_agree.svelte: same as above

src/routes/events/[event_id]/(pres_mgmt)/presenter/[presenter_id]/+page.svelte

@@ -364,20 +364,20 @@
             <!-- Yes... This is a duplicate of what is shown when they press "Presenter Files" button. It can be cleaned up later. -->
             {#if $ae_loc.trusted_access || $events_loc.auth__kv.presenter[$lq__event_presenter_obj?.event_presenter_id]}
                 <Comp_event_files_upload
-                    class_li="border border-gray-300 rounded-md p-2 bg-gray-100 hover:bg-gray-200"
+                    class_li="border border-surface-200-800 rounded-xl p-4 bg-surface-50-900 hover:bg-surface-100-900 transition-colors duration-200"
                     link_to_type="event_presenter"
                     link_to_id={$lq__event_presenter_obj?.event_presenter_id}
                 >
                     {#snippet label()}
                         <span>
                             <div class="text-lg">
-                                <span class="fas fa-upload"></span>
+                                <span class="fas fa-upload" aria-hidden="true"></span>
                                 <strong class=""
                                     >Upload presenter (speaker) specific files</strong
                                 >
                             </div>
                             <div
-                                class="text-sm text-gray-600 dark:text-gray-400 italic"
+                                class="text-sm opacity-60 italic"
                             >
                                 <strong
                                     >Presenter (speaker) presentation files only</strong