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/config/config_test.go

@@ -834,12 +834,13 @@ func TestEgressAllowlistWarning(t *testing.T) {
 			// to be able to read back which networks are open.
 			assert.Contains(t, logged, "10.0.0.0/8")
 			assert.Contains(t, logged, "127.0.0.0/8")
-			// What stays shut. Asserted on the clause naming the
-			// wider set rather than on "Link-local" alone, so the
-			// string cannot narrow back to link-local only while
-			// the always-blocked set covers ULA, CGNAT and two
-			// public metadata addresses as well.
-			assert.Contains(t, logged, "metadata endpoints outside it")
+			// What stays shut is the whole unconditional set, not
+			// link-local alone; a public metadata address is not in
+			// it, so a listed block covering it opens it.
+			assert.Contains(t, logged, "blocked unconditionally")
+			assert.Contains(t, logged, "168.63.129.16 is reachable")
+			// The listed blocks need not be private or reserved.
+			assert.NotContains(t, logged, "private/reserved")
 		})
 	}
 }