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/af_packet_cve_2017_7308/NOTICE.md

@@ -16,14 +16,14 @@ Original advisory + writeup:
 Upstream fix: mainline 4.11 / stable 4.10.6 (March 2017).
 Branch backports: 4.10.6 / 4.9.18 / 4.4.57 / 3.18.49.
 
-## IAMROOT role
+## SKELETONKEY role
 
 x86_64-only. Userns gives CAP_NET_RAW; `socket(AF_PACKET, SOCK_RAW)`
 + TPACKET_V3 with overflowing tp_block_size triggers the integer
 overflow + heap spray via 200 raw skbs on lo. Best-effort cred-race
 finisher (64 child workers polling geteuid). Offset table covers
 Ubuntu 16.04/4.4 and 18.04/4.15; other kernels via the
-`IAMROOT_AFPACKET_OFFSETS` env var.
+`SKELETONKEY_AFPACKET_OFFSETS` env var.
 
 `--full-chain` engages the shared modprobe_path finisher with
 stride-seeded sk_buff data-pointer overwrite.