release v0.7.1: arm64-static binary + per-module arch_support

Two additions on top of v0.7.0:

1. skeletonkey-arm64-static is now published alongside the existing
   x86_64-static binary. Built native-arm64 in Alpine via GitHub's
   ubuntu-24.04-arm runner pool (free for public repos as of 2024).
   install.sh auto-picks it based on 'uname -m'; SKELETONKEY_DYNAMIC=1
   fetches the dynamic build instead. Works on Raspberry Pi 4+, Apple
   Silicon Linux VMs, AWS Graviton, Oracle Ampere, Hetzner ARM, etc.

   .github/workflows/release.yml refactor: the previous single
   build-static-x86_64 job becomes a build-static matrix with two
   entries (x86_64-static on ubuntu-latest, arm64-static on
   ubuntu-24.04-arm). Both share the same Alpine container + build
   recipe.

2. .arch_support field on struct skeletonkey_module — honest per-module
   labeling of which architectures the exploit() body has been verified
   on. Three categories:

     'any' (4 modules): pwnkit, sudo_samedit, sudoedit_editor,
       pack2theroot. Purely userspace; arch-independent.

     'x86_64' (1 module): entrybleed. KPTI prefetchnta side-channel;
       x86-only by physics. Already source-gated (returns
       PRECOND_FAIL on non-x86_64).

     'x86_64+unverified-arm64' (26 modules): kernel exploitation
       code. The bug class is generic but the exploit primitives
       (msg_msg sprays, finisher chain, struct offsets) haven't been
       confirmed on arm64. detect() still works (just reads ctx->host);
       only the --exploit path is in question.

   --list now has an ARCH column (any / x64 / x64?) and the footer
   prints 'N arch-independent (any)'.
   --module-info prints 'arch support: <value>'.
   --scan --json adds 'arch_support' to each module record.

This is the honest 'arm64 works for detection on every module +
exploitation on 4 of them today; the rest await empirical arm64
sweep' framing — not pretending the kernel exploits already work
there, but not blocking the arm64 binary on that either. arm64
users get the full triage workflow + a handful of userspace exploits
out of the box, plus a clear roadmap for the rest.

Future work to promote modules from 'x86_64+unverified-arm64' to
'any': add an arm64 Vagrant box (generic/debian12-arm64 etc.) to
tools/verify-vm/ and run a verification sweep on Apple Silicon /
ARM Linux hardware.

modules/cgroup_release_agent_cve_2022_0492/skeletonkey_modules.c

@@ -404,6 +404,7 @@ const struct skeletonkey_module cgroup_release_agent_module = {
     .detect_yara    = cgroup_release_agent_yara,
     .detect_falco   = cgroup_release_agent_falco,
     .opsec_notes    = "unshare(CLONE_NEWUSER|CLONE_NEWNS), mount cgroup v1 at /tmp/skeletonkey-cgroup-mnt, write payload path to release_agent file at cgroup root, echo 1 to notify_on_release in subdir, add PID to cgroup.procs and exit. Payload at /tmp/skeletonkey-cgroup-payload.sh runs as init-namespace root when cgroup empties, dropping setuid /tmp/skeletonkey-cgroup-sh. Audit-visible via unshare + mount(cgroup) + open/write of release_agent. Cleanup callback removes /tmp/skeletonkey-cgroup-* and umounts.",
+    .arch_support   = "x86_64+unverified-arm64",
 };
 
 void skeletonkey_register_cgroup_release_agent(void)