include: one folder per subsystem, and includes that name it

Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".

Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

.claude/memory/schunix-text-rendering.md

@@ -8,7 +8,7 @@ metadata:
   modified: 2026-08-08T22:45:34.934Z
 ---
 
-Built 2026-08-09. `include/text.h` + `kernel/dev/text.c`. Nexoniarz: "using ANSI
+Built 2026-08-09. `include/gfx/text.h` + `kernel/dev/text.c`. Nexoniarz: "using ANSI
 fonts in 2026 is a not funny joke."
 
 **The font was never the problem — the grid was.** The console indexes
@@ -44,7 +44,7 @@ a useful side-by-side.
 
 ## Traps hit
 
-- `include/font.h` **defines** `font_data` rather than declaring it, so
+- `include/gfx/font.h` **defines** `font_data` rather than declaring it, so
   including it from a second file duplicates the symbol under `-fno-common`.
   text.c declares `extern unsigned char font_data[256][16];` instead; the header
   is generated data and is better left alone.