Record networking and DMA development progress

Add the current OS source tree, build scripts, system image layout, and development notes covering DMA page allocation, e1000 bring-up, net API dispatch, and DHCP work in progress.

CODE/UTSM/drr/drr_stub.c

@@ -0,0 +1,37 @@
+#include <utsm/drr.h>
+#include <utsm/log.h>
+
+static const u64 g_root_key[4] = {
+    0x4452525554534d31ULL,
+    0xfeedfacecafebeefULL,
+    0x0123456789abcdefULL,
+    0xfedcba9876543210ULL
+};
+
+void drr_stub_init(void) {
+}
+
+const u64 *drr_get_root_key(void) {
+    return g_root_key;
+}
+
+u64 drr_recovery_generation(void) {
+    return 1;
+}
+
+void drr_report_fault(const char *reason) {
+    log_error("[DRR] fault reported");
+    log_error(reason);
+}
+
+void drr_log_write_intent(u32 segment_slot, u64 offset, u64 len) {
+    UTSM_UNUSED(segment_slot);
+    UTSM_UNUSED(offset);
+    UTSM_UNUSED(len);
+}
+
+void drr_log_write_commit(u32 segment_slot, u64 offset, u64 len) {
+    UTSM_UNUSED(segment_slot);
+    UTSM_UNUSED(offset);
+    UTSM_UNUSED(len);
+}