Add Typed Display Settings Administration

Implements admin-only Display settings with generation-checked
Apply, Save, Load, Defaults, and Reset operations across the web UI,
CLI, SSH dispatcher, and local UI owner. Adds bounded HTTP handling,
session-isolated operation results, browser lifecycle support, and
comprehensive host tests and documentation.

tests/web_cookie_auth/test.c

@@ -143,6 +143,9 @@ static void auth_reset(void) {
 #ifdef HOST_NETWORK
 #include "network_settings_test.c"
 #endif
+#ifdef HOST_DISPLAY
+#include "display_settings_test.c"
+#endif
 
 int main(void) {
     assert(store_tests() == 0); auth_reset();
@@ -302,6 +305,9 @@ int main(void) {
 #endif
 #ifdef HOST_NETWORK
     network_settings_tests();
+#endif
+#ifdef HOST_DISPLAY
+    display_settings_tests();
 #endif
     return 0;
 }