feat(panic): FUCK [panic] mode=strict|fallback + realtest image variant

- UTSM panic_full returns in fallback mode (logs [PANIC:FALLBACK] + code + hit
  count); panic_halt keeps always-halt sites (CPU exception, VMM-E11 LA57,
  VMM-E15 DSK jump, UTSM-E42 test hook). Call sites given safe continuations.
- Mode passed to DSK/FirstInit/login/desktop via DSK_BOOT_FLAG_PANIC_FALLBACK;
  DKM kernel_api.panic / kern.log.panic return to driver; ext4 fatal aborts the
  op via setjmp/longjmp and DSK falls back to FAT32 ESP.
- build.ps1/Makefile: dev=strict, release=fallback, new realtest (release
  options + strict); default -Variant all; serialized iso packing under -j.
- Fix '*/' inside comments (dkm.h, kernel_api.h, bus.c) that broke the build.
- Includes pending work: dkm_bus service bus, mt7920/wlan drivers, desktop
  files/startmenu/prank, pe-tools, diskinfo, docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

CODE/DKM/virtio_net/virtio_net.c

@@ -784,7 +784,7 @@ static int virtio_net_tx_stub(void *ctx, const void *packet, u32 length) {
     (void)ctx; (void)packet;
     log_hex("[virtio_net] tx stub hit, len=", length);
     g_log->panic("VNET-E01 TX VIRTQUEUE NOT IMPLEMENTED (stub tx called)");
-    return 0;
+    return -1;
 }
 
 static int virtio_net_rx_poll_stub(void *ctx, void *buffer, u32 capacity, u32 *out_length) {