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/kernel_args.h

@@ -0,0 +1,51 @@
+/*
+ * kernel_args.h — boot command-line argument structure and defaults
+ *
+ * KernelArgs is populated by the UEFI loader from LoadOptions (or the
+ * one-shot StarForthBootArgs NVRAM variable) and carried to kernel_main
+ * via BootInfo.args.  All fields have safe defaults so the kernel boots
+ * normally when no arguments are present.
+ */
+
+#ifndef STARKERNEL_KERNEL_ARGS_H
+#define STARKERNEL_KERNEL_ARGS_H
+
+#include <stdint.h>
+
+/* ---- Buffer size -------------------------------------------------------- */
+/* Shared by BootInfo.args.raw, the NVRAM variable payload, and cmdline.c.  */
+#define KERNEL_ARGS_CMDLINE_MAX  512
+
+/* ---- Defaults ----------------------------------------------------------- */
+#define KARGS_DEFAULT_STACK_SIZE   (2ULL  * 1024ULL * 1024ULL)            /* 2 MB  */
+#define KARGS_DEFAULT_HEAP_SIZE    (2ULL  * 1024ULL * 1024ULL * 1024ULL)  /* 2 GB  */
+#define KARGS_DEFAULT_LOG_LEVEL    2    /* warn — quiet by default; --log-level=info/debug re-enables ECW word-execution tracing */
+#define KARGS_DEFAULT_RUN_DOE      0
+
+/* ---- Log level constants ------------------------------------------------ */
+#define KARGS_LOG_DEBUG  0
+#define KARGS_LOG_INFO   1
+#define KARGS_LOG_WARN   2
+#define KARGS_LOG_ERROR  3
+
+/* ---- REBOOT escape hatch ------------------------------------------------ */
+/* Max consecutive REBOOT attempts before the escape hatch fires.
+ * On the Nth boot the counter is checked; if >= REBOOT_MAX_TRIES the
+ * REBOOT word drops to REPL instead of calling ResetSystem. */
+#define REBOOT_MAX_TRIES  3
+
+/* ---- Struct ------------------------------------------------------------ */
+typedef struct {
+    /* Memory sizing — 0 means "use default" */
+    uint64_t stack_size;   /* --stack=<N>[KMG] */
+    uint64_t heap_size;    /* --heap=<N>[KMG]  */
+
+    /* Runtime behaviour */
+    int      run_doe;      /* --doe            (0 = off) */
+    int      log_level;    /* --log-level=...  (KARGS_LOG_*)  */
+
+    /* Raw unparsed cmdline; always NUL-terminated */
+    char     raw[KERNEL_ARGS_CMDLINE_MAX];
+} KernelArgs;
+
+#endif /* STARKERNEL_KERNEL_ARGS_H */