Fix CSS variables, missing utility classes, API hardening, and audit log UX

- base.css: add --lt-border/--lt-surface aliases so dashboard.css respects
  theme instead of using hardcoded fallback colors
- base.css: add lt-select-sm/lt-input-sm compact size variants (used in 15+
  places), lt-msg-danger alias for lt-msg-error, lt-form-hint--warn,
  lt-font-mono utility class
- audit_log.php: cap ?limit= at 500 to prevent DoS via oversized queries
- ApiKeysView.php: replace deprecated execCommand('copy') with lt.copy();
  add integer casts on api_key_id in id attr and data-id
- AuditLogView.php: rebuild pagination with windowed prev/next/ellipsis
  pattern matching DashboardView; integer cast on user_id select option

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

assets/css/base.css

@@ -85,6 +85,8 @@
   --lt-cyan:        var(--accent-cyan);
   --lt-success:     var(--accent-green);
   --lt-text-primary: var(--accent-green);
+  --lt-border:      var(--border-color);
+  --lt-surface:     var(--bg-card);
 
   /* Legacy aliases — keeps all existing component HTML working */
   --terminal-green:       var(--accent-green);
@@ -966,11 +968,26 @@ select option:checked {
   clip-path: none;
 }
 
+/* Compact size variants for inline filter bars and tight layouts */
+.lt-select-sm {
+  font-size: 0.7rem;
+  padding: 0.25rem 1.6rem 0.25rem 0.5rem;
+  width: auto;
+}
+.lt-input-sm {
+  font-size: 0.7rem;
+  padding: 0.25rem 0.5rem;
+  width: auto;
+}
+
 .lt-form-hint {
   font-size: 0.63rem;
   color: var(--text-muted);
   letter-spacing: 0.04em;
 }
+.lt-form-hint--warn { color: var(--accent-amber); }
+
+.lt-font-mono { font-family: var(--font-mono); }
 
 /* Search */
 .lt-search { position: relative; }
@@ -1586,12 +1603,14 @@ select option:checked {
 }
 .lt-msg::before { flex-shrink: 0; font-weight: 700; }
 
-.lt-msg-error   { color: var(--accent-red);   background: var(--accent-red-dim);   border-left-color: var(--accent-red); }
+.lt-msg-error,
+.lt-msg-danger  { color: var(--accent-red);   background: var(--accent-red-dim);   border-left-color: var(--accent-red); }
 .lt-msg-success { color: var(--accent-green);  background: var(--accent-green-dim); border-left-color: var(--accent-green); }
 .lt-msg-warning { color: var(--accent-amber);  background: var(--accent-amber-dim); border-left-color: var(--accent-amber); }
 .lt-msg-info    { color: var(--accent-cyan);   background: var(--accent-cyan-dim);  border-left-color: var(--accent-cyan); }
 
-.lt-msg-error::before   { content: '✗'; }
+.lt-msg-error::before,
+.lt-msg-danger::before  { content: '✗'; }
 .lt-msg-success::before { content: '✓'; }
 .lt-msg-warning::before { content: '!'; }
 .lt-msg-info::before    { content: 'i'; }