fix: reject private IPs after DNS resolution (SSRF/DNS-rebinding)

The SSRF guard only checked the host string, so an attacker-owned domain
resolving to 169.254.169.254 / 10.x (DNS rebinding, TOCTOU) bypassed it.
Add a reqwest dns::Resolve (SafeResolver) that drops resolved addresses in
private ranges, wired into all four crawler/analysis clients — it fires per
connection so it also covers redirect hops. Also close the is_private_ip
IPv6-embedding gaps (IPv4-compatible ::/96, NAT64 64:ff9b::/96, 6to4
2002::/16 all now unwrap to the embedded IPv4).

Bump to 0.124.10.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/bin/crawler.rs

@@ -126,6 +126,8 @@ async fn main() -> anyhow::Result<()> {
         .redirect(mangalord::crawler::safety::safe_redirect_policy(
             (*allowlist).clone(),
         ))
+        // Reject hosts that resolve to private/internal IPs (DNS rebinding).
+        .dns_resolver(mangalord::crawler::safety::safe_dns_resolver())
         .cookie_provider(cookie_jar);
     if let Some(ua) = &user_agent {
         http_builder = http_builder.user_agent(ua);