fix(proxy-subscriptions): allow local/loopback proxy-subscription fetch URLs (#10416)

* fix(proxy-subscriptions): allow local/loopback proxy-subscription fetch URLs

The subscription fetch guard (fetchGuard.ts) unconditionally blocked all
loopback/private IP ranges as SSRF protection, but the same feature already
permits loopback for the routing half (coreEndpoint.ts's
ALLOWED_LOCAL_CORE_HOSTS) — so an operator could route traffic through a
loopback core but could not fetch a proxy list from a loopback HTTP server.

Make the fetch guard local-first by reusing the existing
areLocalProviderUrlsAllowed() policy (default ON) from
outboundUrlGuardPolicy.ts: loopback/private hosts are now allowed as fetch
targets by default, while cloud-metadata/link-local (169.254.0.0/16, incl.
169.254.169.254 IMDS) and the unspecified address stay blocked
unconditionally, mirroring the provider-validation guard's "block-metadata"
mode. Callers that want the old strict behavior can pass
{ allowLocal: false }.

Closes #10158.

* fix(proxy-subscriptions): unwrap IPv4-mapped IPv6 + full fe80::/10 range (#10416)

The #10158 SSRF guard left two gaps on the IPv6 side: an IPv4-mapped IPv6
literal (::ffff:a.b.c.d) skipped IPv4 range checking entirely, and the
link-local check only matched strings literally prefixed with "fe80"
instead of the full fe80::/10 range (fe80:: - febf:ffff::), so fe90::,
febf:ffff::, etc. were wrongly allowed through.

isIpv6Blocked() now unwraps mapped IPv4 addresses (both the dotted-quad
and WHATWG-normalized hex-group forms) and re-checks them against the
IPv4 rules, and link-local detection parses the first hex group's numeric
value against the 0xfe80-0xfebf range instead of a string prefix.

---------

Co-authored-by: adevwithpurpose <adevwithpurpose@users.noreply.github.com>

docs/openapi.yaml

@@ -8597,7 +8597,12 @@ components:
           type: string
         url:
           type: string
-          description: Redacted subscription URL.
+          description: >-
+            Redacted subscription URL. May be a local/loopback address
+            (e.g. `http://127.0.0.1:8080/list`) — local-first fetch targets
+            are allowed by default (`OMNIROUTE_ALLOW_LOCAL_PROVIDER_URLS`);
+            cloud-metadata / link-local endpoints (169.254.0.0/16) are always
+            blocked.
         enabled:
           type: boolean
         mode: