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

README.md

@@ -157,6 +157,11 @@ private and reserved ranges — RFC 1918, loopback, CGNAT, link-local and
 the rest — are refused, which stops a target from being used to make
 webhooker probe the network it sits in.
 
+Besides the private and reserved ranges, the default blocklist refuses
+public cloud metadata addresses: currently only `168.63.129.16`, Azure's
+WireServer, which serves an Azure VM its credentials. Because it is a
+public address, listing it in `ALLOWED_EGRESS_CIDRS` reopens it.
+
 That default is also inconvenient for the thing webhooker is mostly
 for: taking a public webhook and forwarding it to something on your own
 network. A container on the same Docker network, a box on `10.x`, a
@@ -195,15 +200,16 @@ Two things this setting cannot do:
   the list is always an allowlist; an empty list (the default) means
   every private and reserved range stays refused. Note that
   `0.0.0.0/0` gets you most of the way there anyway, per above.
-- **It cannot open link-local, or a cloud metadata endpoint that
-  discloses credentials or user data.** An address is on the list below
-  when both of these hold: the provider fixes it, so it cannot collide
-  with anything you run; and reaching it hands out credentials, user
-  data or bootstrap material. Those stay blocked no matter what you
-  list, including when you list them outright or list a supernet such
-  as `0.0.0.0/0`, `::/0`, `fd00::/8` or `100.64.0.0/10`. Treat this as
-  best effort rather than a guarantee — it is a hand-maintained list
-  and the caveat below the table applies:
+- **It cannot open link-local, or a cloud metadata endpoint at a
+  non-public address that discloses credentials or user data.** An
+  address is on the list below when it is not a public address and both
+  of these hold: the provider fixes it, so it cannot collide with
+  anything you run; and reaching it hands out credentials, user data or
+  bootstrap material. Those stay blocked no matter what you list,
+  including when you list them outright or list a supernet such as
+  `0.0.0.0/0`, `::/0`, `fd00::/8` or `100.64.0.0/10`. Treat this as best
+  effort rather than a guarantee — it is a hand-maintained list and the
+  caveat below the table applies:
 
   | Blocked unconditionally | What it is |
   | ----------------------- | ---------- |
@@ -242,7 +248,8 @@ Two things this setting cannot do:
   encodings, which the default blocklist does not match. A publicly
   routable metadata address is not listed here, because nothing on this
   list can be reopened and blocking one that way would leave you no
-  escape hatch at all.
+  escape hatch at all; Azure's `168.63.129.16` is refused by the default
+  blocklist instead, as described above.
 
   This list is not exhaustive of every cloud's metadata address — if
   yours is not here, do not allowlist the block that contains it.