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/src/capsule/capsule_vm_hooks.c

@@ -0,0 +1,127 @@
+/*
+  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.
+*/
+
+/**
+ * capsule_vm_hooks.c - VM Hook Implementations for Capsule Birth (M7.1)
+ *
+ * Concrete implementations of the three function pointers required by
+ * capsule_birth_set_hooks():
+ *
+ *   capsule_exec_hook      -- wraps vm_interpret()
+ *   capsule_dict_hash_hook -- xxhash64 walk of the live dictionary
+ *   capsule_vm_alloc_hook  -- allocates and initialises a fresh VM
+ *
+ * Call capsule_vm_hooks_register() once during VM bootstrap (after
+ * register_forth79_words) to wire everything up.
+ */
+
+#include "starkernel/capsule_birth.h"
+#include "starkernel/capsule_loader.h"
+#include "starkernel/xxhash64.h"
+#include "vm.h"
+#include "platform_alloc.h"
+#include "word_source/include/mama_forth_words.h"
+#ifdef __STARKERNEL__
+#include "starkernel/hal/hal.h"  /* sk_hal_host_services() */
+#endif
+
+/*===========================================================================
+ * exec hook  ( vm_ctx, code, code_len ) -> 0 on success
+ *===========================================================================*/
+
+static int capsule_exec_hook(void *vm_ctx, const char *code, uint64_t code_len) {
+    return capsule_exec_payload(vm_ctx, (const uint8_t *)code, code_len);
+}
+
+/*===========================================================================
+ * dict hash hook  ( vm_ctx ) -> uint64_t
+ *
+ * Walks the live dictionary linked list and hashes each word's name and
+ * execution heat.  Provides a cheap, deterministic snapshot of dictionary
+ * state for parity logging.
+ *===========================================================================*/
+
+static uint64_t capsule_dict_hash_hook(void *vm_ctx) {
+    VM *vm = (VM *)vm_ctx;
+    if (!vm) return 0;
+
+    XXHash64State state;
+    xxhash64_reset(&state, 0);
+
+    DictEntry *entry = vm->latest;
+    while (entry) {
+        /* Hash: word name */
+        xxhash64_update(&state, entry->name, entry->name_len);
+        /* Hash: execution heat (captures runtime activity level) */
+        xxhash64_update(&state, &entry->execution_heat,
+                        sizeof(entry->execution_heat));
+        entry = entry->link;
+    }
+
+    return xxhash64_digest(&state);
+}
+
+/*===========================================================================
+ * vm alloc hook  () -> void* (VM*)
+ *
+ * Allocates a fresh VM on the heap, initialises it fully (including word
+ * registration and physics subsystems), and returns it as an opaque pointer.
+ * Returns NULL on allocation failure.
+ *===========================================================================*/
+
+static void *capsule_vm_alloc_hook(void) {
+    VM *vm = (VM *)sf_malloc(sizeof(VM));
+    if (!vm) return (void *)0;
+
+#ifdef __STARKERNEL__
+    vm_init_with_host(vm, sk_hal_host_services());
+#else
+    vm_init(vm);
+#endif
+
+    /* vm_init sets vm->error if memory allocation failed internally */
+    if (vm->error) {
+        vm_cleanup(vm);
+        sf_free(vm);
+        return (void *)0;
+    }
+
+    /* Enable interpreter — child VMs skip sk_vm_bootstrap_parity, must set manually */
+    vm_enable_interpreter(vm);
+
+    /* Register STOP + EXEC via the dedicated function in mama_forth_words.c.
+     * Do NOT pass mama_word_stop / mama_word_exec as function-pointer arguments
+     * here: cross-TU function-pointer loads generate R_X86_64_REX_GOTPCRELX,
+     * which the PE32+ linker resolves by dereferencing the function address
+     * (reading machine-code bytes) instead of loading the address itself. */
+    register_child_vm_words(vm);
+
+    return (void *)vm;
+}
+
+/*===========================================================================
+ * Registration
+ *===========================================================================*/
+
+/**
+ * capsule_vm_hooks_register - Wire the three hooks into the capsule subsystem.
+ *
+ * Must be called after vm_init() completes on Mama's VM, before any capsule
+ * birth or experiment operations.
+ */
+void capsule_vm_hooks_register(void) {
+    capsule_birth_set_hooks(
+        capsule_exec_hook,
+        capsule_dict_hash_hook,
+        capsule_vm_alloc_hook
+    );
+}