Kernel.nw: first pass by claude (Intro + Overview chapters)

70 %claude: blocks covering Introduction (motivations, Plan 9 kernel,
lineage figure, other kernels) and Overview (OS principles, syscall
interface with per-group annotations, helloraw.c/helloraw.s/minishell.c
concrete examples, Raspberry Pi hardware, ARM CPU/PSR/MMU/coprocessors,
I/O devices with VideoCore GPU/framebuffer, memory-mapped I/O,
C and assembly, code organization, software architecture, boot overview,
memory overview, syscall overview with systab, book structure).

Also added \label{chap:...} to all chapters and the Fred Brooks
epigraph to Core Data Structures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: aryx