feat: add screenshot app

programs/lib/libjpegwrite/Makefile

@@ -0,0 +1,66 @@
+# Makefile for libjpegwrite (JPEG encoding via stb_image_write) on MontaukOS
+# Copyright (c) 2026 Daniel Hammer
+
+MAKEFLAGS += -rR
+.SUFFIXES:
+
+# ---- Toolchain ----
+
+TOOLCHAIN_PREFIX := $(shell cd ../../.. && pwd)/toolchain/local/bin/x86_64-elf-
+ifneq ($(wildcard $(TOOLCHAIN_PREFIX)gcc),)
+    CC := $(TOOLCHAIN_PREFIX)gcc
+    AR := $(TOOLCHAIN_PREFIX)ar
+else
+    CC := gcc
+    AR := ar
+endif
+
+# ---- Paths ----
+
+LIBC_INC := ../../include/libc
+PROG_INC := ../../include
+OBJDIR   := obj
+
+# ---- Compiler flags ----
+
+CFLAGS := \
+    -std=gnu11 \
+    -g -O2 -pipe \
+    -Wall \
+    -Wno-unused-parameter \
+    -Wno-unused-function \
+    -nostdinc \
+    -ffreestanding \
+    -fno-stack-protector \
+    -fno-stack-check \
+    -fno-PIC \
+    -ffunction-sections \
+    -fdata-sections \
+    -fno-tree-loop-distribute-patterns \
+    -m64 \
+    -march=x86-64 \
+    -msse \
+    -msse2 \
+    -mno-red-zone \
+    -mcmodel=small \
+    -I $(PROG_INC) \
+    -isystem $(LIBC_INC) \
+    -isystem $(shell $(CC) -print-file-name=include)
+
+# ---- Target ----
+
+TARGET := libjpegwrite.a
+
+.PHONY: all clean
+
+all: $(TARGET)
+
+$(TARGET): $(OBJDIR)/stb_image_write_impl.o
+	$(AR) rcs $@ $^
+
+$(OBJDIR)/stb_image_write_impl.o: stb_image_write_impl.c Makefile
+	@mkdir -p $(OBJDIR)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+clean:
+	rm -rf $(OBJDIR) $(TARGET)

programs/lib/libjpegwrite/stb_image_write_impl.c

@@ -0,0 +1,23 @@
+/*
+ * stb_image_write_impl.c
+ * Single compilation unit for stb_image_write JPEG encoder on MontaukOS
+ * Copyright (c) 2026 Daniel Hammer
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+/* Only enable JPEG writing. */
+#define STBI_WRITE_NO_STDIO
+
+/* Route allocations through libc (which uses MontaukOS heap). */
+#define STBIW_MALLOC(sz)         malloc(sz)
+#define STBIW_FREE(p)            free(p)
+#define STBIW_REALLOC(p, newsz)  realloc(p, newsz)
+#define STBIW_MEMMOVE(d, s, n)   memmove(d, s, n)
+
+#define STBIW_ASSERT(x)  ((void)(x))
+
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include <gui/stb_image_write.h>