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/capsule_runcap.h

@@ -0,0 +1,78 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  Licensed under the StarForth License, Version 1.0
+*/
+
+/**
+ * capsule_runcap.h - RUNCAP: runtime capsule construction from thumbdrive
+ * content (FABRIC-2.md §F.6/§F.18).
+ *
+ * A user's identity source (raw FORTH init/personality text, minted by
+ * MINT into a home-blocks drive's identity_src region) never exists at
+ * build time, so it can never appear in the compile-time-baked capsule
+ * directory. This builds a heap-only, single-entry CapsuleDirHeader +
+ * CapsuleDesc + CapsuleNameEntry + arena from that region and hands it to
+ * the existing, unmodified capsule_birth_baby() -- no new birth mechanism,
+ * per §F.6's own trace ("capsule_birth_baby() is already generic").
+ *
+ * Does not verify the caller has already run CERTVERIFY -- that's the
+ * caller's responsibility (WIREBIND, not yet built). This function's own
+ * job is narrow: read the region, construct the directory, birth it.
+ */
+
+#ifndef STARKERNEL_CAPSULE_RUNCAP_H
+#define STARKERNEL_CAPSULE_RUNCAP_H
+
+#ifdef __STARKERNEL__
+
+#include <stdint.h>
+#include "starkernel/capsule_run.h"   /* CapsuleRunResult */
+#include "starkernel/vm_uuid.h"       /* VMUuid */
+#include "starkernel/homeblocks_sig.h" /* homeblocks_sig_t */
+
+struct blkio_dev;
+
+/**
+ * capsule_runcap_birth - Birth a VM from a home-blocks drive's own
+ * identity_src region.
+ *
+ * Reads sig->identity_src_devblocks devblocks starting at
+ * sig->identity_src_offset. The first devblock is the identity's own
+ * user_identity_seed_t record (MINT, §F.8) and is skipped here -- RUNCAP
+ * only cares about the FORTH source that follows it. Refuses cleanly
+ * (CAPSULE_RUN_ERR_INVALID) if identity_src_offset is 0 (never minted) or
+ * identity_src_devblocks < 2 (no source content beyond the seed record).
+ *
+ * The heap-allocated directory/descriptor/name/arena are never freed --
+ * deliberate, matching kernel_main.c's own compile-time-directory-to-heap
+ * copy at Mama's own birth (also never freed): a VM's IDENTITY exec reads
+ * directly from this arena, and nothing in this codebase frees capsule
+ * arenas after a successful birth today.
+ *
+ * @param dev         Already-open block device for the attached drive.
+ * @param sig         Already-verified homeblocks_sig_t read from it.
+ * @param vm_name     Symbolic name for the new VM (becomes both the
+ *                    capsule's own single directory entry name and the
+ *                    VM registry name).
+ * @param parent      Who is birthing this VM (FABRIC-2.md §H.12 step 7) --
+ *                    passed straight through to capsule_birth_baby().
+ * @param out_vm_id   Output: assigned VM ID.
+ * @param out_vm_ctx  Output: new VM context (may be NULL if not needed).
+ * @return CAPSULE_RUN_OK on success, error code otherwise.
+ */
+CapsuleRunResult capsule_runcap_birth(
+    struct blkio_dev      *dev,
+    const homeblocks_sig_t *sig,
+    const char             *vm_name,
+    VMUuid                  parent,
+    VMUuid                 *out_vm_id,
+    void                  **out_vm_ctx
+);
+
+#endif /* __STARKERNEL__ */
+
+#endif /* STARKERNEL_CAPSULE_RUNCAP_H */