rename: IAMROOT → SKELETONKEY across the entire project

Breaking change. Tool name, binary name, function/type names,
constant names, env vars, header guards, file paths, and GitHub
repo URL all rebrand IAMROOT → SKELETONKEY.

Changes:
  - All "IAMROOT" → "SKELETONKEY" (constants, env vars, enum
    values, docs, comments)
  - All "iamroot" → "skeletonkey" (functions, types, paths, CLI)
  - iamroot.c → skeletonkey.c
  - modules/*/iamroot_modules.{c,h} → modules/*/skeletonkey_modules.{c,h}
  - tools/iamroot-fleet-scan.sh → tools/skeletonkey-fleet-scan.sh
  - Binary "iamroot" → "skeletonkey"
  - GitHub URL KaraZajac/IAMROOT → KaraZajac/SKELETONKEY
  - .gitignore now expects build output named "skeletonkey"
  - /tmp/iamroot-* tmpfiles → /tmp/skeletonkey-*
  - Env vars IAMROOT_MODPROBE_PATH etc. → SKELETONKEY_*

New ASCII skeleton-key banner (horizontal key icon + ANSI Shadow
SKELETONKEY block letters) replaces the IAMROOT banner in
skeletonkey.c and README.md.

VERSION: 0.3.1 → 0.4.0 (breaking).

Build clean on Debian 6.12.86. `skeletonkey --version` → 0.4.0.
All 24 modules still register; no functional code changes — pure
rename + banner refresh.

modules/dirty_pipe_cve_2022_0847/detect/auditd.rules

@@ -13,14 +13,14 @@
 # Watch /etc/passwd, /etc/shadow, /etc/sudoers, /etc/sudoers.d/* for
 # any modification by non-root — the Dirty Pipe payload typically
 # overwrites these to gain root.
--w /etc/passwd      -p wa -k iamroot-dirty-pipe
--w /etc/shadow      -p wa -k iamroot-dirty-pipe
--w /etc/sudoers     -p wa -k iamroot-dirty-pipe
--w /etc/sudoers.d   -p wa -k iamroot-dirty-pipe
+-w /etc/passwd      -p wa -k skeletonkey-dirty-pipe
+-w /etc/shadow      -p wa -k skeletonkey-dirty-pipe
+-w /etc/sudoers     -p wa -k skeletonkey-dirty-pipe
+-w /etc/sudoers.d   -p wa -k skeletonkey-dirty-pipe
 
 # Watch every splice() syscall — combined with the file watches above
 # this catches the canonical exploit shape. (High volume on servers
 # using nginx/HAProxy; consider scoping with -F gid!=33 -F gid!=99 to
 # exclude web servers.)
--a always,exit -F arch=b64 -S splice -k iamroot-dirty-pipe-splice
--a always,exit -F arch=b32 -S splice -k iamroot-dirty-pipe-splice
+-a always,exit -F arch=b64 -S splice -k skeletonkey-dirty-pipe-splice
+-a always,exit -F arch=b32 -S splice -k skeletonkey-dirty-pipe-splice