v0.3.1: --dump-offsets tool + NOTICE.md per module

The README has been claiming "each module credits the original CVE
reporter and PoC author in its NOTICE.md" since v0.1.0, but only
copy_fail_family actually shipped one. Fixed.

  modules/<name>/NOTICE.md (×19 new + 1 existing): per-module
    research credit covering CVE ID, discoverer, original advisory
    URL where public, upstream fix commit, IAMROOT's role.

  iamroot.c: new --dump-offsets subcommand. Resolves kernel offsets
    via the existing core/offsets.c four-source chain (env →
    /proc/kallsyms → /boot/System.map → embedded table), then emits
    a ready-to-paste C struct entry for kernel_table[]. Run once
    as root on a target kernel build; upstream via PR. Eliminates
    fabricating offsets — every shipped entry traces back to a
    `iamroot --dump-offsets` invocation on a real kernel.

  docs/OFFSETS.md: documents the --dump-offsets workflow.
  CVES.md: notes the NOTICE.md convention + offset dump tool.

  iamroot.c: bump IAMROOT_VERSION 0.3.0 → 0.3.1.

modules/overlayfs_setuid_cve_2023_0386/NOTICE.md

@@ -0,0 +1,25 @@
+# NOTICE — overlayfs_setuid (CVE-2023-0386)
+
+## Vulnerability
+
+**CVE-2023-0386** — overlayfs `copy_up` preserves the setuid bit
+across mount-namespace boundaries → host root via a setuid carrier
+placed in the lower layer.
+
+## Research credit
+
+Discovered and disclosed by **Xkaneiki**, January 2023.
+
+Public PoC + writeup:
+<https://github.com/xkaneiki/CVE-2023-0386>
+
+Upstream fix: mainline 6.2-rc6 (commit `4f11ada10d0a`, Jan 2023).
+Branch backports: 5.10.169 / 5.15.92 / 6.1.11.
+
+## IAMROOT role
+
+Distro-agnostic — no per-kernel offsets, no race. Places a setuid
+binary in an overlay lower, mounts via fuse-overlayfs userns trick,
+executes from the upper layer to inherit the setuid bit + root euid.
+
+Auditd rules cover overlayfs mounts and unexpected setuid copy-ups.