fix(suspended): tolerate startup DNS failure + use docker_dns resolvers

If the upstream container isn't up when haproxy-manager starts (e.g. when
haproxy is recreated before whp-suspended), the default `init-addr libc` mode
makes haproxy refuse to start — taking down the whole proxy. Switched to
`init-addr last,none` (use last known address, fall back to 0.0.0.0 = DOWN)
and added `resolvers docker_dns` (defined in hap_header.tpl) so the real IP
is picked up once DNS becomes resolvable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/hap_suspended_backend.tpl

@@ -10,4 +10,9 @@ backend bk_suspended
     option http-server-close
     http-request set-header X-Forwarded-Proto https if { ssl_fc }
     http-request set-header X-Forwarded-For %[src]
-    server suspended {{ target }} check inter 30s
+    # init-addr last,none: tolerate startup-time DNS resolution failure
+    # (the upstream container may not be up yet when haproxy-manager starts).
+    # resolvers docker_dns: re-resolve via Docker's embedded DNS at 127.0.0.11
+    # so the server picks up the real IP once the upstream becomes available
+    # (the docker_dns block is defined in hap_header.tpl).
+    server suspended {{ target }} check inter 30s init-addr last,none resolvers docker_dns