release v0.9.4: drift unblock, fragnesia range fix, infra docs

- Sync docs/CVE_METADATA.json + KEV_CROSSREF.md to match the
  hand-applied core/cve_metadata.c entries from v0.9.3. Nightly
  drift-check (red since 2026-05-25) now passes. Pintheft's CWE
  landed as CWE-787 from NVD (was NULL in the hand-applied entry).
- Fix fragnesia (CVE-2026-46300) range table. Per NVD: bug entered
  at 5.11 SKBFL_SHARED_FRAG, vulnerable through 5.15.207 / 6.1.173 /
  6.6.140 / 6.12.90 / 6.18.32 / 7.0.9, fixed at .208/.174/.141/
  .91/.33/.10. Prior table had one entry {7,0,9} — off-by-one and
  missing every other backport. Added predates-5.11 introduction gate
  + test row.
- Update tools/verify-vm/README.md to document the v0.9.x infra:
  mainline kernel pinning via kernel.ubuntu.com, per-module
  provisioner hooks, two-phase prep→reboot→verify with post-reboot
  kernel confirmation, GRUB_DEFAULT pinning.
- Add curl fallback for NVD lookups in refresh-cve-metadata.py.
  Mirrors the CISA path's existing fallback. Prevents the silent
  Python urlopen hang seen during v0.9.3 prep (55-min stuck on
  CLOSE_WAIT socket; 30s timeout never fired).

tests/test_detect.c

@@ -332,6 +332,12 @@ static void run_all(void)
 		&dirtydecrypt_module, &h_ubuntu_24_userns_ok,
 		SKELETONKEY_OK);
 
+	/* fragnesia: SKBFL_SHARED_FRAG marker added in 5.11; kernels before
+	 * that predate the buggy skb_try_coalesce() code → OK */
+	run_one("fragnesia: kernel 4.4 predates 5.11 SKBFL_SHARED_FRAG → OK",
+		&fragnesia_module, &h_kernel_4_4,
+		SKELETONKEY_OK);
+
 	/* fragnesia: userns disabled → XFRM gate closed → PRECOND_FAIL */
 	run_one("fragnesia: userns_allowed=false → PRECOND_FAIL",
 		&fragnesia_module, &h_pre7_no_userns_no_dbus,