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/nft_fwd_dup_cve_2022_25636/NOTICE.md

@@ -17,12 +17,12 @@ Original writeup:
 Upstream fix: mainline 5.17 (commit `fa54fee62954`, Feb 2022).
 Branch backports: 5.16.11 / 5.15.25 / 5.10.102 / 5.4.181.
 
-## IAMROOT role
+## SKELETONKEY role
 
 userns+netns reach. Hand-rolled nfnetlink batch: NEWTABLE →
 NEWCHAIN with `NFT_CHAIN_HW_OFFLOAD` → NEWRULE with 16 immediates
 + fwd, overruning `action.entries[1]`. msg_msg cross-cache groom
-into kmalloc-512 with `IAMROOT_FWD` tags.
+into kmalloc-512 with `SKELETONKEY_FWD` tags.
 
 `--full-chain` extends with stride-seeded forged action_entry
 overwrite aimed at modprobe_path via the shared finisher.