feat(security): add global toggle to allow private/internal URL resolution

Adds security.allow_private_urls / HERMES_ALLOW_PRIVATE_URLS toggle so
users on OpenWrt routers, TUN-mode proxies (Clash/Mihomo/Sing-box),
corporate split-tunnel VPNs, and Tailscale networks — where DNS resolves
public domains to 198.18.0.0/15 or 100.64.0.0/10 — can use web_extract,
browser, vision URL fetching, and gateway media downloads.

Single toggle in tools/url_safety.py; all 23 is_safe_url() call sites
inherit automatically. Cached for process lifetime.

Cloud metadata endpoints stay ALWAYS blocked regardless of the toggle:
169.254.169.254 (AWS/GCP/Azure/DO/Oracle), 169.254.170.2 (AWS ECS task
IAM creds), 169.254.169.253 (Azure IMDS wire server), 100.100.100.200
(Alibaba), fd00:ec2::254 (AWS IPv6), the entire 169.254.0.0/16
link-local range, and the metadata.google.internal / metadata.goog
hostnames (checked pre-DNS so they can't be bypassed on networks where
those names resolve to local IPs).

Supersedes #3779 (narrower HERMES_ALLOW_RFC2544 for the same class of
users).

Co-authored-by: kshitijk4poor <82637225+kshitijk4poor@users.noreply.github.com>

hermes_cli/config.py

@@ -840,6 +840,7 @@ DEFAULT_CONFIG = {
 
     # Pre-exec security scanning via tirith
     "security": {
+        "allow_private_urls": False,  # Allow requests to private/internal IPs (for OpenWrt, proxies, VPNs)
         "redact_secrets": True,
         "tirith_enabled": True,
         "tirith_path": "tirith",