feat: add laptop/display brightness modulation

programs/include/montauk/capabilities.h

@@ -38,6 +38,7 @@ namespace caps {
         {"log_read",      montauk::abi::CAP_LOG_READ},
         {"system_image",  montauk::abi::CAP_SYSTEM_IMAGE},
         {"compositor",    montauk::abi::CAP_COMPOSITOR},
+        {"brightness",    montauk::abi::CAP_BRIGHTNESS},
     };
 
     // Never implied by "all": each must be named explicitly in a grant.