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/zuse_eligibility.c

@@ -0,0 +1,107 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  Licensed under the StarForth License, Version 1.0
+*/
+
+#ifndef __STARKERNEL__
+#error "zuse_eligibility.c is kernel-only"
+#endif
+
+#include "starkernel/zuse_eligibility.h"
+#include "starkernel/zuse_eligibility_list.h"
+#include "block_subsystem.h" /* compute_crc64(), blk_meta_zone_read/write */
+#include <string.h>
+#include <stddef.h>
+
+/* Read and validate one devblock of the chain. Mirrors
+ * capsule_zuse_boot.c's genesis_marker_read() convention exactly: magic
+ * mismatch, version mismatch, and CRC mismatch are all merged into a
+ * single -1 ("treat as absent/corrupt, not present") -- the fence region
+ * is never zeroed at format time (block_subsystem.c's blk_commit_format()
+ * only zeroes BAM/reloc), so blank foreign bytes and genuine corruption
+ * are indistinguishable and must be handled identically here. */
+static int list_devblock_read(uint32_t devblock_from_top, zuse_eligibility_devblock_t *out) {
+    if (blk_meta_zone_read(devblock_from_top, (uint8_t *)out) != 0) return -1;
+    if (out->magic != ZUSE_ELIGIBILITY_LIST_MAGIC) return -1;
+    if (out->version != ZUSE_ELIGIBILITY_LIST_VERSION) return -1;
+    if (out->count > ZUSE_ELIGIBILITY_ENTRIES_PER_DEVBLOCK) return -1;
+    uint64_t want_crc = compute_crc64((const uint8_t *)out,
+                                       offsetof(zuse_eligibility_devblock_t, crc));
+    if (want_crc != out->crc) return -1;
+    return 0;
+}
+
+static int list_devblock_write(uint32_t devblock_from_top, zuse_eligibility_devblock_t *blk) {
+    blk->crc = compute_crc64((const uint8_t *)blk, offsetof(zuse_eligibility_devblock_t, crc));
+    return blk_meta_zone_write(devblock_from_top, (const uint8_t *)blk) == 0 ? 0 : -1;
+}
+
+int zuse_eligibility_is_member(const uint8_t pubkey[32]) {
+    uint32_t devblock = ZUSE_ELIGIBILITY_LIST_HEAD_DEVBLOCK;
+    zuse_eligibility_devblock_t blk;
+
+    for (;;) {
+        if (list_devblock_read(devblock, &blk) != 0) return 0; /* fail-closed */
+        for (uint32_t i = 0; i < blk.count; i++) {
+            if (memcmp(blk.entries[i], pubkey, 32) == 0) return 1;
+        }
+        if (blk.next_devblock_from_top == ZUSE_ELIGIBILITY_LIST_NO_NEXT) return 0;
+        devblock = blk.next_devblock_from_top;
+    }
+}
+
+int zuse_eligibility_add(const uint8_t pubkey[32]) {
+    uint32_t devblock = ZUSE_ELIGIBILITY_LIST_HEAD_DEVBLOCK;
+    zuse_eligibility_devblock_t blk;
+
+    if (list_devblock_read(devblock, &blk) != 0) {
+        /* List doesn't exist yet (blank fence, or this is genuinely the
+         * first entry ever added) -- create the head devblock fresh. */
+        memset(&blk, 0, sizeof(blk));
+        blk.magic  = ZUSE_ELIGIBILITY_LIST_MAGIC;
+        blk.version = ZUSE_ELIGIBILITY_LIST_VERSION;
+        blk.count = 1;
+        blk.next_devblock_from_top = ZUSE_ELIGIBILITY_LIST_NO_NEXT;
+        memcpy(blk.entries[0], pubkey, 32);
+        return list_devblock_write(devblock, &blk);
+    }
+
+    /* Walk the existing chain: bail out early (idempotent success) if
+     * already present, otherwise track the tail devblock to append to. */
+    for (;;) {
+        for (uint32_t i = 0; i < blk.count; i++) {
+            if (memcmp(blk.entries[i], pubkey, 32) == 0) return 0; /* already eligible */
+        }
+        if (blk.next_devblock_from_top == ZUSE_ELIGIBILITY_LIST_NO_NEXT) break;
+        devblock = blk.next_devblock_from_top;
+        if (list_devblock_read(devblock, &blk) != 0) return -1; /* corrupt mid-chain */
+    }
+
+    if (blk.count < ZUSE_ELIGIBILITY_ENTRIES_PER_DEVBLOCK) {
+        memcpy(blk.entries[blk.count], pubkey, 32);
+        blk.count++;
+        return list_devblock_write(devblock, &blk);
+    }
+
+    /* Tail devblock is full -- chain a fresh one drawn from the
+     * already-reserved fence budget, one devblock_from_top past the
+     * current tail (blk_meta_zone_write() itself refuses any offset at
+     * or beyond the on-disk meta_fence_blocks reservation, so an
+     * exhausted budget surfaces here as an ordinary write failure). */
+    uint32_t new_devblock = devblock + 1;
+    zuse_eligibility_devblock_t new_blk;
+    memset(&new_blk, 0, sizeof(new_blk));
+    new_blk.magic   = ZUSE_ELIGIBILITY_LIST_MAGIC;
+    new_blk.version = ZUSE_ELIGIBILITY_LIST_VERSION;
+    new_blk.count   = 1;
+    new_blk.next_devblock_from_top = ZUSE_ELIGIBILITY_LIST_NO_NEXT;
+    memcpy(new_blk.entries[0], pubkey, 32);
+    if (list_devblock_write(new_devblock, &new_blk) != 0) return -1;
+
+    blk.next_devblock_from_top = new_devblock;
+    return list_devblock_write(devblock, &blk);
+}