test harness: kernel_range unit tests + coverage report + register_all helper

Three coupled improvements to the test harness:

1. New tests/test_kernel_range.c — 32 pure unit tests covering
   kernel_range_is_patched(), skeletonkey_host_kernel_at_least(),
   and skeletonkey_host_kernel_in_range(). These are the central
   comparison primitives every module routes through; a regression
   in any of them silently mis-classifies entire CVE families. Tests
   cover exact boundary, one-below, mainline-only, multi-LTS,
   between-branch, and NULL-safety cases. Builds and runs
   cross-platform (no Linux syscalls).

2. tests/test_detect.c additions:
   - mk_host(base, major, minor, patch, release) builder so new
     fingerprint-based tests don't duplicate 14-line struct literals
     to override one (major, minor, patch) triple.
   - Post-run coverage report that iterates the runtime registry and
     warns about modules without at least one direct test row. Output
     is informational (no CI fail) so coverage grows incrementally.
   - 7 new boundary tests for the kernel_patched_from entries added
     by tools/refresh-kernel-ranges.py (commit 8de46e2):
       - af_unix_gc 6.4.12 → VULNERABLE / 6.4.13 → OK
       - vmwgfx 5.10.127 → OK
       - nft_set_uaf 5.10.179 → OK / 6.1.27 → OK
       - nft_payload 5.10.162 → OK
       - nf_tables 5.10.209 → OK

3. core/registry_all.c — extracts the 27-line 'call every
   skeletonkey_register_<family>()' enumeration from skeletonkey.c
   into a shared helper. skeletonkey.c main() now calls
   skeletonkey_register_all_modules() once; the detect-test main()
   does the same. Kept in its own translation unit so registry.c
   stays standalone for the lean kernel_range unit-test binary
   (which links core/ only, no modules).

Makefile: builds two test binaries now —
  skeletonkey-test     — detect() integration tests (full corpus)
  skeletonkey-test-kr  — kernel_range unit tests (core/ only)
'make test' runs both.

Verification:
  - macOS: 32/32 kernel_range tests pass; detect tests skipped
    (non-Linux platform, stubbed bodies).
  - Linux (docker gcc:latest): 32/32 kernel_range + 51/51 detect.
    Coverage report identifies 2 modules without direct tests
    (copy_fail, entrybleed) out of 31 registered.

Test counts: 44 -> 83 (+39).

core/registry_all.c

@@ -0,0 +1,46 @@
+/*
+ * SKELETONKEY — canonical "register every module family" enumeration.
+ *
+ * Kept in its own translation unit so registry.c stays standalone:
+ * the kernel_range unit-test binary links registry.c (for the basic
+ * register / count / find API) without pulling in every module's
+ * symbol. The main binary and detect-integration test link this
+ * file too and get the full lineup.
+ *
+ * Adding a new module is one new register_<family>() declaration in
+ * registry.h plus one call below — the integration test picks it up
+ * via skeletonkey_register_all_modules() in its main().
+ */
+
+#include "registry.h"
+
+void skeletonkey_register_all_modules(void)
+{
+    skeletonkey_register_copy_fail_family();
+    skeletonkey_register_dirty_pipe();
+    skeletonkey_register_entrybleed();
+    skeletonkey_register_pwnkit();
+    skeletonkey_register_nf_tables();
+    skeletonkey_register_overlayfs();
+    skeletonkey_register_cls_route4();
+    skeletonkey_register_dirty_cow();
+    skeletonkey_register_ptrace_traceme();
+    skeletonkey_register_netfilter_xtcompat();
+    skeletonkey_register_af_packet();
+    skeletonkey_register_fuse_legacy();
+    skeletonkey_register_stackrot();
+    skeletonkey_register_af_packet2();
+    skeletonkey_register_cgroup_release_agent();
+    skeletonkey_register_overlayfs_setuid();
+    skeletonkey_register_nft_set_uaf();
+    skeletonkey_register_af_unix_gc();
+    skeletonkey_register_nft_fwd_dup();
+    skeletonkey_register_nft_payload();
+    skeletonkey_register_sudo_samedit();
+    skeletonkey_register_sequoia();
+    skeletonkey_register_sudoedit_editor();
+    skeletonkey_register_vmwgfx();
+    skeletonkey_register_dirtydecrypt();
+    skeletonkey_register_fragnesia();
+    skeletonkey_register_pack2theroot();
+}