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_set_uaf_cve_2023_32233/NOTICE.md

@@ -20,12 +20,12 @@ Upstream fix: mainline 6.4-rc4 (commit `c1592a89942e9`, May 2023).
 Branch backports: 6.3.2 / 6.2.15 / 6.1.28 / 5.15.111 / 5.10.180 /
 5.4.243 / 4.19.283.
 
-## IAMROOT role
+## SKELETONKEY role
 
 Hand-rolled nfnetlink batch: NEWTABLE → NEWCHAIN (base, LOCAL_OUT
 hook) → NEWSET (ANON|EVAL|CONSTANT) → NEWRULE (nft_lookup
 referencing the set by `NFTA_LOOKUP_SET_ID`) → DELSET → DELRULE
-in the same transaction. msg_msg cg-512 spray with `IAMROOT_SET`
+in the same transaction. msg_msg cg-512 spray with `SKELETONKEY_SET`
 tags.
 
 `--full-chain` forges a freed-set with `set->data = kaddr` at the