Add a VSH-only allowlist for real-loading flash0 modules, sceVshCommonUtil stub and sceVshBridge

Load and start VSH's kernel modules before booting vshmain.prx

A few flash0 modules (vshbridge.prx, paf.prx, common_gui.prx,
common_util.prx) should run for real once we know we're
actually booting the VSH rather than a game, since our fakes are unlikely
to be good substitutes for the genuine thing.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01PSNaZnHCjmryS3ziVN9gZU

headless/Headless.cpp

@@ -137,6 +137,7 @@ std::string NativeLoadSecret(std::string_view nameOfSecret) {
 int printUsage(const CommandLineOptions &options, const char *progname, const char *reason) {
 	options.PrintUsage(progname, reason);
 	fprintf(stderr, "  --ir                  use ir interpreter\n");
+	fprintf(stderr, "  --flash0=DIR          use DIR as flash0: instead of the bundled assets (e.g. a real dump)\n");
 	return 1;
 }