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/README.md

@@ -0,0 +1,58 @@
+# src/
+
+Hosted StarForth VM implementation (compiled by the root `Makefile`).
+Bare-metal kernel sources live in `src/starkernel/`; FORTH word
+implementations in `src/word_source/`; the test harness in
+`src/test_runner/`; platform shims in `src/platform/`.
+
+**Entry point / interpreter core**
+- `main.c` — CLI entry point, VM init, DoE mode dispatch.
+- `vm.c` — interpreter loop, stacks, dictionary state (the central
+  runtime file).
+- `vm_api.c` — external VM API implementation.
+- `vm_bootstrap.c` — VM bootstrap initialization.
+- `vm_debug.c` — debugging utilities.
+- `vm_time.c` — time-related VM operations.
+- `vm_internal.h` — internal-only declarations shared across the `vm_*.c`
+  files, not part of the public `include/vm_api.h` surface.
+- `repl.c` — REPL read-eval-print loop.
+- `cli.c` — CLI argument parsing.
+- `io.c` — I/O operations.
+- `log.c` — logging infrastructure.
+
+**Memory / dictionary / blocks**
+- `memory_management.c` — dictionary allocator.
+- `dictionary_management.c` — dictionary allocation and search.
+- `dictionary_heat_optimization.c` — Loop #1 execution-heat tracking.
+- `word_registry.c` — word registration system.
+- `block_subsystem.c` — logical→physical block mapper.
+- `blkio_file.c`, `blkio_ram.c`, `blkio_factory.c` — block I/O backends
+  (file-backed, RAM-backed) and the factory that selects between them.
+- `stack_management.c` — stack operations.
+
+**Physics-driven adaptive runtime (7 feedback loops)**
+- `physics_runtime.c` — main physics coordinator.
+- `physics_hotwords_cache.c` — Loop #1 hot-words caching.
+- `physics_metadata.c` — per-word metadata tracking.
+- `physics_pipelining_metrics.c` — Loop #4 word-transition prediction.
+- `physics_execution_hooks.c` — execution instrumentation.
+- `rolling_window_of_truth.c` — Loop #2 circular execution-history buffer.
+- `inference_engine.c` — Loops #5/#6, statistical inference (window-width,
+  decay-slope).
+- `ssm_jacquard.c` — L8 Jacquard steady-state mode selector; consumes
+  `compudynamics.c` for tuning-word/config lookups.
+- `compudynamics.c` — generic compudynamics module (`cd_tuning_word()`,
+  `cd_tuning_vm()`); the score/UCB/reward/weight constants for the L8
+  adaptive table live here, not in `ssm_jacquard.c`.
+- `heartbeat_export.c` — heartbeat metrics export (CSV export function
+  itself not yet implemented — see `docs/working/architecture/heartbeat_csv_export.md`).
+
+**Math / measurement**
+- `math_portable.c` — portable math functions.
+- `profiler.c` — performance profiling.
+- `doe_metrics.c` — Design of Experiments metrics (2^7 factorial).
+
+Any `.bak` file alongside a `.c` file here (`doe_metrics.c.bak`,
+`inference_engine.c.bak`, `vm.c.bak`) is a pre-edit backup left by a past
+maintenance script (see `scripts/remove_loop_conditionals.sh`), not a
+build input.