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_attrib.h

@@ -0,0 +1,64 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  This file is part of the StarForth project.
+
+  Licensed under the StarForth License, Version 1.0 (the "License");
+  you may not use this file except in compliance with the License.
+
+  You may obtain a copy of the License at:
+      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
+
+  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  express or implied, including but not limited to the warranties of
+  merchantability, fitness for a particular purpose, and noninfringement.
+
+  See the License for the specific language governing permissions and
+  limitations under the License.
+*/
+
+/**
+ * log_attrib.h - "Which VM is currently executing" for log persistence
+ * attribution (FABRIC-3.md §XXVI follow-on, Step 4, 2026-09-13)
+ *
+ * log_message() (shim.c) is a global function called from hundreds of
+ * existing sites -- most with no VM in scope at all (boot, PCI, xHCI,
+ * driver code). Rather than thread a VM parameter through every one of
+ * those call sites (a large, invasive change for no benefit to the ones
+ * that genuinely have no VM), vm_interpret() (vm_core.c, the single
+ * dispatch entry point for ALL FORTH execution -- interactive lines,
+ * LOAD'd block content, and every VM-EXEC/MSG-DELIVER dispatch into a
+ * target VM) sets this at entry and restores the previous value at exit,
+ * save/restore style so nested vm_interpret() calls (VM-EXEC dispatching
+ * into a different VM's own dictionary, mid-interpret) attribute
+ * correctly to whichever VM is actually running at the moment
+ * log_message() fires -- not the outermost caller.
+ *
+ * NULL means "no VM is currently interpreting" -- boot sequence, PCI/
+ * xHCI/driver code, anything running outside a vm_interpret() call frame.
+ * log_message()'s own persistence hook (shim.c) treats NULL as the fixed
+ * "HADES" pseudo-source, matching the console's own existing
+ * "[HADES][LEVEL]" prefix convention for exactly this class of message.
+ */
+
+#ifndef STARKERNEL_LOG_ATTRIB_H
+#define STARKERNEL_LOG_ATTRIB_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct VM;
+
+/* vm_log_attributed_vm - The VM whose dictionary context is currently
+ * executing, or NULL if none (see this header's own doc comment). */
+struct VM *vm_log_attributed_vm(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* STARKERNEL_LOG_ATTRIB_H */