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>

v3/src/test_runner/modules/README.md

@@ -0,0 +1,26 @@
+# src/test_runner/modules/
+
+Per-category test files, one per FORTH-79 word category plus
+integration/stress/adversarial suites, run in this order by
+`test_runner.c` (POST order).
+
+**Word-category tests** (validate each `src/word_source/*.c` file):
+`arithmetic_words_test.c`, `mixed_arithmetic_words_test.c`,
+`stack_words_test.c`, `control_words_test.c`, `defining_words_tests.c`,
+`memory_words_test.c`, `return_stack_words_test.c`, `double_words_test.c`,
+`logical_words_test.c`, `io_words_test.c`, `string_words_test.c`,
+`block_words_test.c`, `format_words_test.c`, `system_words_test.c`,
+`dictionary_words_test.c`, `dictionary_manipulation_words_test.c`,
+`vocabulary_words_test.c`, `starforth_words_test.c`,
+`mama_forth_words_test.c`, `acl_words_test.c`.
+
+**Cross-cutting tests**:
+- `integration_tests.c` — multi-word interaction tests.
+- `stress_tests.c` — load/volume tests.
+- `break_me_tests.c` — adversarial/fuzzing tests.
+
+Note: not every `src/word_source/*.c` file has a dedicated test module
+here (e.g. `defer_words.c`, `log_words.c`, `inference_words.c`,
+`lifecycle_words_hosted.c`, `editor_words.c` are exercised indirectly via
+integration tests or the `tools/hermes_*.sh` smoke tests rather than a
+standalone `*_test.c` module).