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>

tools/README.md

@@ -7,7 +7,7 @@ toolchain.
 
 | File | Purpose |
 |------|---------|
-| `mkcapsule.c` | Assembles `.4th` capsule files into `capsule_generated.c` baked into the kernel image. Invoked automatically by `Makefile.starkernel`. |
+| `mkcapsule.c` | Assembles `.4th` capsule files into `capsule_generated.c` baked into the kernel image. Invoked automatically by `kernel/Makefile`. |
 | `mkcapsule` | Compiled host binary (rebuilt on demand). |
 | `ttftest.c` | Host TTF glyph-rendering test — font rasterization unit tests, no QEMU needed. |
 | `pe_reloc_gen.py` | Generates PE32+ relocation tables for the UEFI loader. |
@@ -21,7 +21,7 @@ toolchain.
 
 ```bash
 # Invoked automatically by the kernel build:
-make -f Makefile.starkernel ARCH=amd64 clean qemu
+make -f kernel/Makefile ARCH=amd64 clean qemu
 
 # Manual invocation (for inspection):
 ./tools/mkcapsule capsules/ build/amd64/kernel/capsule_generated.c
@@ -33,5 +33,5 @@ type `(m)` to `init.4th` and `(p)` to everything else.
 ## See also
 
 - [`capsules/README.md`](../capsules/README.md) — capsule file format and block namespace
-- [`Makefile.starkernel`](../Makefile.starkernel) — kernel build system
+- [`kernel/Makefile`](../kernel/Makefile) — kernel build system
 - [Project root](../README.md)

tools/ttftest.c

@@ -25,7 +25,7 @@
 #include <string.h>
 #include <time.h>
 
-#include "../include/starkernel/ttf.h"
+#include "../kernel/include/starkernel/ttf.h"
 
 typedef struct {
     uint32_t codepoint;