Default-block Azure WireServer's public address (closes #245)

Add 168.63.129.16 (Azure WireServer) to blockedNetworks, the default
blocklist, not alwaysBlockedNetworks: it is public unicast, so an
operator who lists it in ALLOWED_EGRESS_CIDRS can reach it again. The
refusal message, the allowlist startup warning, the README and the
comments no longer call every blocked address private/reserved, and
no longer claim the allowlist cannot open any metadata endpoint.

Sources:
- https://learn.microsoft.com/en-us/azure/virtual-network/what-is-ip-address-168-63-129-16
- https://learn.microsoft.com/en-us/azure/virtual-machines/metadata-security-protocol/overview

Deviation: 147.75.207.243 (Equinix Metal) is not added; Equinix
documents only a hostname, and the service was sunset on 2026-06-30.

Model: opus-5-5

internal/delivery/ssrf_allowlist_test.go

@@ -390,6 +390,41 @@ func TestGuardAllowlist_PublicUnaffected(t *testing.T) {
 	}
 }
 
+// TestGuardAllowlist_AzureWireServerReopenable covers Azure's
+// WireServer, a public address that serves VM credentials. The
+// default guard refuses it, but because it is public it sits in
+// the default blocklist rather than the unconditional set, so an
+// operator who lists it can reach it.
+func TestGuardAllowlist_AzureWireServerReopenable(t *testing.T) {
+	t.Parallel()
+
+	const wireServerIP = "168.63.129.16"
+
+	target := "http://" + wireServerIP + "/?comp=versions"
+
+	defaultGuard := delivery.NewTestGuard()
+
+	err := defaultGuard.ValidateTargetURL(context.Background(), target)
+	require.Error(t, err,
+		"WireServer must be refused with no allowlist set",
+	)
+	assert.NotContains(t, err.Error(), metadataRefusalClause,
+		"WireServer must be refused by the default blocklist, "+
+			"which an allowlist can override",
+	)
+
+	assertDialRefused(t, defaultGuard, target)
+
+	listed := delivery.NewTestGuard(
+		netip.MustParsePrefix(wireServerIP + "/32"),
+	)
+
+	assert.NoError(t,
+		listed.ValidateTargetURL(context.Background(), target),
+		"an operator who lists WireServer must be able to reach it",
+	)
+}
+
 // TestGuardCheckIP_BothPathsShareOneDecision asserts that the
 // validator and the dialer are not two policies that happen to
 // agree: both are defined in terms of checkIP, so the exported