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/src/arch/aarch64/README.md

@@ -0,0 +1,17 @@
+# src/starkernel/arch/aarch64/
+
+AArch64 architecture support for LithosAnanke.
+
+- `arch.c` — architecture init entry point.
+- `apic.c` — GIC (Generic Interrupt Controller) stub, named `apic.c` to
+  match the shared per-arch file-naming convention across
+  amd64/aarch64/riscv64. Satisfies the common `apic_init()`/`apic_eoi()`
+  call sites without real GIC bring-up yet; deferred to a later milestone.
+- `timer.c` — architected timer setup (heartbeat tick source).
+- `interrupts.c` — exception vector table setup and interrupt dispatch.
+- `boot.S` — early boot assembly.
+- `isr.S` — interrupt service routine stubs.
+
+No `kernel_entry.S` — aarch64 uses a different UEFI loader entry path
+(`clang`/`lld-link` COFF target, since GCC cannot produce an aarch64 PE
+image; see `Makefile.starkernel`).