feat(FN-3558): add action-gate reload endpoint for reloadable exempt-tools

Adds a reload endpoint for exempt agent tools (FN-3731), enabling runtime refresh of action-gate configuration without restart, with corresponding dashboard routes and tests. Also fixes mobile nav colors to properly respect design tokens (FN-3558).

Fusion-Task-Id: FN-3558

packages/dashboard/app/components/MobileNavBar.css

@@ -23,7 +23,7 @@
      the indicator (PWA standalone) and the bar meets the executor status bar
      flush — its `bottom` already adds these same terms. */
   padding-bottom: calc(env(safe-area-inset-bottom, 0px) + var(--standalone-bottom-gap));
-  box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.15);
+  box-shadow: var(--shadow-md);
 }
 
 @media (max-width: 768px) {
@@ -125,7 +125,7 @@
   position: fixed;
   inset: 0;
   z-index: 90;
-  background: rgba(0, 0, 0, 0.5);
+  background: color-mix(in srgb, var(--bg) 50%, transparent);
   animation: mobile-more-backdrop-in 0.2s ease;
 }
 
@@ -202,7 +202,7 @@
 }
 
 .mobile-more-item:active {
-  background: var(--surface-hover);
+  background: var(--surface-hover, color-mix(in srgb, var(--text) 6%, transparent));
 }
 
 .mobile-more-item svg {