Reorganize source tree: kernel/, v3/, v4/ split and board infrastructure

Source tree reorganization:
- Move StarForth v3 engine to v3/ (src/, include/, Makefile)
- Move kernel to kernel/ (src/, include/, linker/, Makefile)
- Create v4/ skeleton for F18-ISA golden model (DECOMPOSITION.md, JUSTIFICATION.md)
- Move FABRIC-0..4.md to docs/fabric/
- Move ONTOLOGY.md and ROADMAP.md to docs/

Board infrastructure:
- Add boards/ser5/, boards/raspi/, boards/milkv/, boards/zynq7020/
- Each board has board.mk (ISA, CPU flags, boot recipe) and README.md
- Root Makefile becomes thin dispatcher: boot_image, all, clean, docs take TARGET
- make boot_image TARGET=SER5|RASPI|MILKV builds one GPT/MBR image per board
- ZYNQ7020 target exists but stops with clear error (ARMv7 port not built yet)
- scripts/mkdiskimage.sh builds disk images for all boards

Docs pipeline:
- docs/book/ with LaTeX master (main.tex) and Makefile
- pandoc converts Markdown to LaTeX at build time
- Two Lua filters: table-widths.lua (wide tables wrap), code-breaks.lua (inline code breaks)
- make docs builds single PDF (754 pages, 0 missing characters)
- make docs TARGET=<board> adds board appendix
- build/docs/<book|board>/meta.tex stamps git commit into PDF

Bug fixes:
- 42 include paths that only worked by accident now use correct relative paths
- clang-18 hardcode replaced with configurable CC variable (fixed aarch64 build)
- Pi 5: kernel_2712.img linked at 0x80000, .bss zeroed, memory reserved
- Doxyfile, .clang-tidy, README.md, Kconfig paths updated

Verified:
- Hosted v3 build passes 1012 tests, 0 failures
- SER5 image boots in QEMU (OVMF), POST passes, K exact (65536 = Q48_ONE)
- Milk-V image boots in QEMU (OpenSBI + U-Boot + bootefi), POST passes
- make clean TARGET=<board> removes only that board and its ISA objects
- make all builds all boards, hosted v3, and docs in one run

Co-authored-by: Junie <junie@jetbrains.com>

kernel/include/starkernel/log.h

@@ -0,0 +1,69 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  Licensed under the StarForth License, Version 1.0
+*/
+
+/**
+ * starkernel/log.h — Kernel-native logger for LithosAnanke
+ *
+ * Provides the same API as the hosted include/log.h so all kernel VM
+ * code calling log_message() works without source changes.
+ *
+ * Output routes through console_puts() → UART → serial log.
+ * Implementation lives in src/starkernel/vm/host/shim.c.
+ *
+ * This header shadows include/log.h for kernel TUs because
+ * -Iinclude/starkernel precedes -Iinclude in KERNEL_CFLAGS and
+ * LOADER_CFLAGS, so #include "log.h" finds this file first.
+ *
+ * No <stdio.h> dependency — freestanding safe.
+ */
+
+#ifndef STARKERNEL_LOG_H
+#define STARKERNEL_LOG_H
+
+/* Forward declaration — matches hosted log.h */
+struct VM;
+
+/* Renamed from LOG_LINE_MAX: vm.h owns that name for the persistent
+ * block-log line width (64, unrelated concept). This is the in-memory log
+ * message-formatting line length; keeping a distinct name removes the
+ * include-order collision that forced a fragile "vm.h before log.h"
+ * convention across the kernel. */
+#ifndef LOG_MSG_LINE_MAX
+#define LOG_MSG_LINE_MAX 256
+#endif
+
+/**
+ * Log levels — identical to the hosted enumeration so kernel VM code
+ * compiled against either header produces compatible call sites.
+ */
+typedef enum {
+    LOG_NONE  = -1, /* Disable all logging */
+    LOG_ERROR =  0, /* Errors only */
+    LOG_WARN,       /* Warnings and errors */
+    LOG_INFO,       /* Informational, warnings, and errors */
+    LOG_TEST,       /* Test results and all above */
+    LOG_DEBUG       /* Full verbosity */
+} LogLevel;
+
+typedef enum {
+    TEST_PASS  = 0,
+    TEST_FAIL,
+    TEST_SKIP,
+    TEST_ERROR
+} TestResult;
+
+void     log_set_level(LogLevel level);
+LogLevel log_get_level(void);
+void     log_message(LogLevel level, const char *fmt, ...);
+void     log_test_result(const char *word_name, TestResult result);
+
+/* TODO: persistent logging via VM-backed ring buffer — stub for now */
+void     log_set_vm(struct VM *vm);
+
+#endif /* STARKERNEL_LOG_H */