fix(contacts): Improve full-screen list height calculation

Adjusted .contacts-list-fullscreen height to better utilize available
screen space by increasing the subtracted value from 200px to 300px
on desktop and from 150px to 340px on mobile.

This accounts for:
- Navbar (~56px)
- Main container padding (~48px)
- Back buttons (~60px)
- Search toolbar (~50px)
- Filter/sort toolbar (~60px)
- Margins between elements (~26px)

Fixes blank space at bottom of Existing Contacts and Pending Contacts pages.

app/templates/contacts_base.html

@@ -216,7 +216,7 @@
 
         /* NEW: Full-screen lists for dedicated pages */
         .contacts-list-fullscreen {
-            height: calc(100vh - 200px);
+            height: calc(100vh - 300px);
             overflow-y: auto;
             -webkit-overflow-scrolling: touch;
             padding: 0;
@@ -332,7 +332,7 @@
             }
 
             .contacts-list-fullscreen {
-                height: calc(100vh - 150px);
+                height: calc(100vh - 340px);
             }
 
             .filter-sort-toolbar {