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.

install.sh

@@ -34,15 +34,15 @@ log()   { printf '[\033[1;36m*\033[0m] %s\n' "$*" >&2; }
 ok()    { printf '[\033[1;32m+\033[0m] %s\n' "$*" >&2; }
 fail()  { printf '[\033[1;31m-\033[0m] %s\n' "$*" >&2; exit 1; }
 
-# Detect architecture
+# Detect architecture. Default to the musl-static binary on both
+# x86_64 and arm64 — works on every libc (glibc 2.x of any version,
+# musl, uclibc); costs ~800 KB extra vs dynamic but eliminates the
+# GLIBC_2.NN portability ceiling that bites on Debian-stable, older
+# RHEL hosts, and Alpine. Set SKELETONKEY_DYNAMIC=1 to fetch the
+# smaller dynamic build (needs glibc >= 2.38 for x86_64 — Ubuntu
+# 24.04 / Debian 13 / RHEL 10).
 arch=$(uname -m)
 case "$arch" in
-    # x86_64 default: the musl-static binary works on every libc
-    # (glibc 2.x of any version, musl, uclibc) — costs ~800 KB extra
-    # vs the dynamic build but eliminates the GLIBC_2.NN portability
-    # ceiling that bit users on Debian-stable / older RHEL hosts.
-    # Set SKELETONKEY_DYNAMIC=1 to fetch the smaller dynamic build
-    # (needs glibc >= 2.38, i.e. Ubuntu 24.04 / Debian 13 / RHEL 10).
     x86_64|amd64)
         if [ "${SKELETONKEY_DYNAMIC:-0}" = "1" ]; then
             target=x86_64
@@ -50,7 +50,13 @@ case "$arch" in
             target=x86_64-static
         fi
         ;;
-    aarch64|arm64)       target=arm64  ;;
+    aarch64|arm64)
+        if [ "${SKELETONKEY_DYNAMIC:-0}" = "1" ]; then
+            target=arm64
+        else
+            target=arm64-static
+        fi
+        ;;
     *) fail "Unsupported architecture: $arch (only x86_64 and arm64 currently)" ;;
 esac
 log "detected arch: $target"