feat: hide CVE checks that arebirrelevant for current arch

CVE_REGISTRY gains an optional fifth field that tags checks as x86-only or
arm-only, untagged entries apply everywhere. The main CVE dispatcher and the
affectedness summary both skip gated entries in default "all CVEs" runs,
removing the noise of arm64 errata on x86 hosts and of x86 CVEs on ARM hosts
across text, json, nrpe and prometheus outputs. Explicit --cve/--variant/--errata
selection bypasses the gate so manual queries still run anywhere.
The gate honours no-hw mode by ignoring the host CPU and keying off the
inspected kernel's architecture only, which handles cross-arch offline
analysis driven by --kernel/--config/--map.

src/libs/200_cpu_affected.sh

@@ -27,6 +27,36 @@ _infer_immune() { eval "[ -z \"\$affected_$1\" ] && affected_$1=1 || :"; }
 # Use for: family-level catch-all fallbacks (Intel L1TF non-whitelist, itlbmh non-whitelist).
 _infer_vuln() { eval "[ -z \"\$affected_$1\" ] && affected_$1=0 || :"; }
 
+# Return 0 (true) if a CVE's arch tag matches the current context (host CPU
+# and/or target kernel), so the check is worth running. Untagged CVEs are
+# always relevant.
+# - In no-hw mode the host CPU is ignored: gate only on target kernel arch.
+# - Otherwise a match on either the host CPU or the target kernel is enough
+#   (they normally agree in live mode; if they disagree, check_kernel_cpu_arch_mismatch
+#    has already forced no-hw, handled by the branch above).
+# Args: $1=cve_id
+# Callers: src/main.sh (CVE dispatch loop), check_cpu_vulnerabilities
+_is_cve_relevant_arch() {
+    local arch
+    arch=$(_cve_registry_field "$1" 5)
+    # Untagged CVE: always relevant
+    [ -z "$arch" ] && return 0
+    case "$arch" in
+        x86)
+            [ "$g_mode" != no-hw ] && is_x86_cpu && return 0
+            is_x86_kernel && return 0
+            return 1
+            ;;
+        arm)
+            [ "$g_mode" != no-hw ] && is_arm_cpu && return 0
+            is_arm_kernel && return 0
+            return 1
+            ;;
+    esac
+    # Unknown tag value: don't gate (fail open)
+    return 0
+}
+
 # Return the cached affected_* status for a given CVE
 # Args: $1=cve_id
 # Returns: 0 if affected, 1 if not affected