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/zuse_eligibility.h

@@ -0,0 +1,56 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  Licensed under the StarForth License, Version 1.0
+*/
+
+/**
+ * zuse_eligibility.h - Read/add/membership-check over the on-disk
+ * elevation eligibility list (FABRIC-2.md §H.5/§H.12 Phase 6,
+ * zuse_eligibility_list.h's zuse_eligibility_devblock_t chain). Zuse
+ * checks zuse_eligibility_is_member() before honoring any
+ * ELEVATE-REQUEST (§H.7/§H.8) -- a gating layer on top of the
+ * message-based elevation trigger, not a replacement for it. Adding an
+ * entry (zuse_eligibility_add()) is meant to be reachable only from a
+ * Zuse-only FORTH word (§H.12 item 19, gated by zuse_session), not
+ * called directly from arbitrary session code.
+ */
+
+#ifndef STARKERNEL_ZUSE_ELIGIBILITY_H
+#define STARKERNEL_ZUSE_ELIGIBILITY_H
+
+#ifdef __STARKERNEL__
+
+#include <stdint.h>
+
+/**
+ * zuse_eligibility_is_member - Check whether pubkey appears anywhere in
+ * the eligibility list chain. Fail-closed: an empty/nonexistent list, a
+ * corrupt/foreign devblock encountered mid-chain, or any I/O error all
+ * read as "not eligible" (0), never "eligible" -- this gates elevation,
+ * so an unreadable list must never be treated as permissive.
+ *
+ * @param pubkey  32-byte Ed25519 public key to look up.
+ * @return        1 if found, 0 otherwise (including on any error).
+ */
+int zuse_eligibility_is_member(const uint8_t pubkey[32]);
+
+/**
+ * zuse_eligibility_add - Add pubkey to the eligibility list, creating
+ * the list's head devblock if it doesn't exist yet and chaining a fresh
+ * devblock onto the tail if the current tail is full. Idempotent: adding
+ * an already-present pubkey is a no-op success, not a duplicate entry.
+ *
+ * @param pubkey  32-byte Ed25519 public key to add.
+ * @return        0 on success (added, or already present), -1 on
+ *                failure (fence write failed, fence budget exhausted, or
+ *                a corrupt devblock was encountered mid-chain).
+ */
+int zuse_eligibility_add(const uint8_t pubkey[32]);
+
+#endif /* __STARKERNEL__ */
+
+#endif /* STARKERNEL_ZUSE_ELIGIBILITY_H */