Fix header overlap, is-hidden missing globally, and CreateTicketView CSS

- base.css: add .lt-main.lt-container combined selector (specificity 0,2,0)
  to prevent responsive .lt-container padding shorthand from overriding
  the fixed-header clearance padding-top — affected all viewports < 1280px
- base.css: add .is-hidden { display: none !important } globally; it was
  only defined in ticket.css so dashboard ticketPreview popup rendered
  as a green box at 0,0 on page load instead of being hidden
- CreateTicketView.php: add dashboard.css to pageStyles so create-ticket-
  meta-grid, lt-form-hint, visibility-groups-list, duplicate-list classes
  are available (they were undefined when only ticket.css was loaded)

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

assets/css/base.css

@@ -366,6 +366,13 @@ hr {
   width: 100%;
   min-width: 0; /* prevent flex overflow on very small viewports */
 }
+/* When both lt-main and lt-container are on the same element, the lt-container
+   shorthand `padding` overrides the lt-main `padding-top` in responsive breakpoints
+   (same cascade specificity, later rule wins). The combined selector has higher
+   specificity (0,2,0 vs 0,1,0) and always wins regardless of source order. */
+.lt-main.lt-container {
+  padding-top: calc(var(--header-height) + var(--space-lg));
+}
 
 .lt-layout {
   display: flex;
@@ -2076,6 +2083,7 @@ select option:checked {
   .lt-main { padding-top: calc(50px + var(--space-md)); }
 
   .lt-container { padding: var(--space-md); }
+  .lt-main.lt-container { padding-top: calc(var(--header-height) + var(--space-md)); }
   .lt-header { padding: 0 var(--space-md); }
   .lt-brand-subtitle { display: none; }
 
@@ -2176,6 +2184,7 @@ select option:checked {
   .lt-main { padding-top: calc(46px + var(--space-sm)); }
 
   .lt-container { padding: var(--space-sm); }
+  .lt-main.lt-container { padding-top: calc(var(--header-height) + var(--space-sm)); }
   .lt-stats-grid { grid-template-columns: 1fr 1fr; gap: var(--space-xs); }
   .lt-stat-card { padding: var(--space-xs) var(--space-sm); }
   .lt-stat-value { font-size: 1.4rem; }
@@ -2272,6 +2281,7 @@ select option:checked {
   .lt-stats-grid { grid-template-columns: repeat(6, 1fr); }
   .lt-grid-4 { grid-template-columns: repeat(4, 1fr); }
   .lt-container { padding: var(--space-xl) var(--space-2xl); }
+  .lt-main.lt-container { padding-top: calc(var(--header-height) + var(--space-xl)); }
 }
 
 
@@ -2383,6 +2393,9 @@ select option:checked {
   border: 0;
 }
 
+/* Global visibility utility — used by JS and all views */
+.is-hidden { display: none !important; }
+
 /* Cursor blink */
 .lt-cursor::after {
   content: '█';