feat: Growable heap, GUI-by-default run, live sysmon, SUB/SUB default login

Kernel / memory:
- mm/kmalloc.c: fix "Heap: Out of memory" under the GUI. The desktop allocates
  three full-screen 32-bit buffers (~11MB) which overflowed the fixed 16MB pool.
  The heap now starts at 32MB and grows on demand from the PMM (16MB regions),
  with region-safe coalescing (only merges physically adjacent blocks) so growth
  never corrupts across separate PMM allocations. Adds heap_get_grow_count().

Build / run:
- Makefile: merge `run-gui` into `run` so `make run` boots into the graphical
  desktop; add `run-headless` (serial-only via QEMU_CMD), bump guest RAM to
  256M, update .PHONY and help.

Configure:
- scripts/kconfig/menuconfig.py: gate the curses UI behind isatty() on stdin and
  stdout so non-interactive `make configure` stops emitting "nocbreak() returned
  ERR" and falls cleanly through to the non-interactive writer.

GUI / userland:
- gui/gui_apps.c: rebuild the System Monitor from hardcoded values into live
  telemetry -- real heap used/total/free with a colour-shifting bar, a scrolling
  heap-utilisation graph, the grow counter, and real PMM RAM figures.
- lazybox `free`: report how many times the heap has grown.

Auth:
- Default login is now SUB / SUB (Kali-style username==password), seeded first
  as the primary uid-0 account and set as the logged-in user; root kept for
  compatibility. Hardcoded "root" defaults (whoami, su, passwd, ssh, sshd
  session) updated to SUB.

Verified: clean build on x86_64/aarch64/armv8i; GUI boots with 0 OOM/0 panic;
auth engine initialises cleanly; `make configure` fallback is clean.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Fh5z6V7nGPbHvqVG5p4CXX

Makefile

@@ -330,7 +330,7 @@ DEPS = $(C_OBJS:.o=.d) $(CPP_OBJS:.o=.d) $(S_OBJS:.o=.d)
 
 .DEFAULT_GOAL := all
 
-.PHONY: all clean run run-fullscreen debug info configure menuconfig config tui nconfig defconfig x86_64_defconfig aarch64_defconfig armv8_defconfig armv8i_defconfig armv81_defconfig arm32_defconfig qemu help
+.PHONY: all clean run run-headless run-fullscreen run-vnc run-server debug info configure menuconfig config tui nconfig defconfig x86_64_defconfig aarch64_defconfig armv8_defconfig armv8i_defconfig armv81_defconfig arm32_defconfig qemu help
 
 all: $(TARGET)
 
@@ -448,24 +448,29 @@ $(IMAGE): $(BUILD_DIR)/boot/boot.bin $(BUILD_DIR)/boot/stage2.bin $(BUILD_DIR)/k
 # -----------------------------------------------------------------------------
 # Execution & Emulation Targets
 # -----------------------------------------------------------------------------
-run qemu: $(TARGET)
-	$(QEMU_CMD)
-
 # -vga std gives the Bochs VBE adapter the kernel drives. vgamem_mb is raised
 # because a 1280x720 32-bit framebuffer needs more than the 8 MB default.
 QEMU_VGA = -device VGA,vgamem_mb=32
 
-run-gui: $(TARGET)
+# `make run` boots straight into the SUB-OS Graphical Desktop Environment. The
+# guest window scales with zoom-to-fit; pass `nogui`/`text` on the kernel
+# command line for the emergency TTY. Use `make run-headless` for serial only.
+run qemu: $(TARGET)
 ifeq ($(ARCH), x86_64)
-	qemu-system-x86_64 -drive format=raw,file=$(IMAGE) \
+	qemu-system-x86_64 -drive format=raw,file=$(IMAGE) -m 256M \
 		-netdev user,id=net0,hostfwd=tcp::2222-:22,hostfwd=tcp::8080-:80 \
 		-device e1000,netdev=net0 $(QEMU_VGA) -display gtk,zoom-to-fit=on -serial stdio
 else ifneq ($(filter $(ARCH), aarch64 arm64),)
-	qemu-system-aarch64 -M virt -cpu cortex-a57 -m 128M -kernel $(BUILD_DIR)/kernel.elf -device virtio-gpu-pci -serial stdio
+	qemu-system-aarch64 -M virt -cpu cortex-a57 -m 256M -kernel $(BUILD_DIR)/kernel.elf -device virtio-gpu-pci -serial stdio
 else
-	qemu-system-arm -M virt -cpu cortex-a15 -m 128M -kernel $(BUILD_DIR)/kernel.elf -device virtio-gpu-pci -serial stdio
+	qemu-system-arm -M virt -cpu cortex-a15 -m 256M -kernel $(BUILD_DIR)/kernel.elf -device virtio-gpu-pci -serial stdio
 endif
 
+# Headless: no graphical window, kernel console on the serial line only. Boot
+# with `nogui` on the kernel command line to reach the TTY in this mode.
+run-headless: $(TARGET)
+	$(QEMU_CMD)
+
 # Fullscreen without distortion: zoom-to-fit scales the guest while preserving
 # its aspect ratio, letterboxing rather than stretching on a wider panel.
 run-fullscreen: $(TARGET)
@@ -521,7 +526,10 @@ help:
 	@echo "  make aarch64_defconfig- Load AArch64 default configuration"
 	@echo "  make armv8i_defconfig - Load ARMv8i (32-bit ARM) default configuration"
 	@echo "  make all [ARCH=...]   - Compile kernel image for selected architecture"
-	@echo "  make qemu [ARCH=...]  - Boot the compiled kernel in QEMU emulator"
+	@echo "  make run [ARCH=...]   - Boot into the SUB-OS Graphical Desktop in QEMU"
+	@echo "  make run-headless     - Boot in QEMU with serial console only (no window)"
+	@echo "  make run-fullscreen   - Boot the desktop in a full-screen QEMU window"
+	@echo "  make run-vnc          - Boot the desktop and expose it over VNC :0"
 	@echo "  make clean            - Remove all compiled objects and disk images"
 	@echo "  make info             - Display build configuration and source metrics"