Phase 7: Pwnkit (CVE-2021-4034) detect-only module

First USERSPACE LPE in IAMROOT (every prior module is kernel). Same
iamroot_module interface — the difference is the affected-version
check is package-version-based rather than kernel-version-based.

- modules/pwnkit_cve_2021_4034/:
  - iamroot_modules.{c,h}: detect() locates setuid pkexec (one of
    /usr/bin/pkexec, /usr/sbin/pkexec, /bin/pkexec, /sbin/pkexec,
    /usr/local/bin/pkexec) and parses 'pkexec --version' output.
    Handles BOTH version-string formats: legacy '0.105'/'0.120'
    (older polkit) AND modern bare-integer '121'/'126' (post-0.121
    rename to single-number scheme). Reports VULNERABLE on parse
    failure (conservative).
  - exploit() returns IAMROOT_PRECOND_FAIL with a 'not yet
    implemented' message; full Qualys-PoC follow-up is the next
    commit. ~200 lines including embedded .so generator.
  - MODULE.md documents the bug, affected ranges, distro backport
    landscape (RHEL 7/8, Ubuntu focal/impish, Debian buster/bullseye
    each have their own backported polkit version).
  - Embedded auditd + sigma detection rules:
    auditd: pkexec watch + execve audit
    sigma:  pkexec invocation + suspicious env (GCONV_PATH, CHARSET)

- core/registry.h adds iamroot_register_pwnkit() declaration.
- iamroot.c main() registers pwnkit.
- Makefile gains the pwnkit family as a separate object set.

Verified end-to-end on kctf-mgr (modern polkit 126):
  iamroot --list  → 8 modules
  iamroot --scan  → pwnkit reports 'version 126 ≥ 0.121 (fixed)'
  iamroot --detect-rules --format=auditd | grep pwnkit → emits

Makefile

@@ -41,10 +41,15 @@ EB_DIR   := modules/entrybleed_cve_2023_0458
 EB_SRCS  := $(EB_DIR)/iamroot_modules.c
 EB_OBJS  := $(patsubst %.c,$(BUILD)/%.o,$(EB_SRCS))
 
+# Family: pwnkit (userspace polkit bug, not kernel)
+PK_DIR   := modules/pwnkit_cve_2021_4034
+PK_SRCS  := $(PK_DIR)/iamroot_modules.c
+PK_OBJS  := $(patsubst %.c,$(BUILD)/%.o,$(PK_SRCS))
+
 # Top-level dispatcher
 TOP_OBJ  := $(BUILD)/iamroot.o
 
-ALL_OBJS := $(TOP_OBJ) $(CORE_OBJS) $(CFF_OBJS) $(DP_OBJS) $(EB_OBJS)
+ALL_OBJS := $(TOP_OBJ) $(CORE_OBJS) $(CFF_OBJS) $(DP_OBJS) $(EB_OBJS) $(PK_OBJS)
 
 .PHONY: all clean debug static help