feat(admin): implement unified submission and newsletter management

Introduce a centralized system to manage all website form submissions and newsletter subscriptions.
- Add `Submission` and `NewsletterSubscription` models with MongoDB schema validation
- Implement `submissionController` and `newsletterSubscriptionController` for CRUD operations and filtering
- Create a unified admin UI for reviewing submissions across different sources (home, request, contact, partnership, newsletter)
- Add database migration scripts for creating collections and indexes
- Refactor partnership inquiry forms to use a fixed field structure
- Update admin navigation and server CORS settings to support PATCH requests

views/admin/partnerships/partials/templates.ejs

@@ -100,9 +100,6 @@
   <div class="card cms-item-card mb-3" data-item="inquiry-field">
     <div class="card-header d-flex justify-content-between align-items-center gap-2 flex-wrap">
       <div class="d-flex align-items-center gap-2">
-        <button type="button" class="drag-handle" title="Drag to reorder">
-          <i class="fas fa-grip-vertical"></i>
-        </button>
         <div>
           <div class="fw-semibold" data-title>Field</div>
           <div class="small text-muted" data-subtitle></div>
@@ -112,9 +109,6 @@
         <button type="button" class="cms-collapse-toggle" data-toggle-item title="Collapse item">
           <i class="fas fa-chevron-down"></i>
         </button>
-        <button type="button" class="cms-remove-button" data-remove-item title="Remove item">
-          <i class="fas fa-trash-alt"></i>
-        </button>
       </div>
     </div>
     <div class="card-body">
@@ -129,7 +123,7 @@
         </div>
         <div class="col-md-4">
           <label class="form-label fw-semibold"><%= inquiryFieldFields.type?.label || "Field type" %></label>
-          <select class="form-select" data-field="type">
+          <select class="form-select" data-field="type" disabled>
             <% (inquiryFieldFields.type?.options || []).forEach((option) => { %>
               <option value="<%= option.value %>"><%= option.label %></option>
             <% }) %>
@@ -144,10 +138,10 @@
           </select>
         </div>
         <div class="col-md-4 d-flex align-items-end">
-          <div class="form-check mb-2">
-            <input class="form-check-input" type="checkbox" data-field="required">
-            <label class="form-check-label fw-semibold"><%= inquiryFieldFields.required?.label || "Required field" %></label>
-          </div>
+            <div class="form-check mb-2">
+              <input class="form-check-input" type="checkbox" data-field="required">
+              <label class="form-check-label fw-semibold"><%= inquiryFieldFields.required?.label || "Required field" %></label>
+            </div>
         </div>
         <div class="col-12" data-options-wrap>
           <div class="cms-editor-group">