feat: DNS-over-HTTPS server endpoint (RFC 8484)

Serve DoH at POST /dns-query on the existing HTTPS proxy (port 443).
Automatically enabled when proxy TLS is active — no config needed.
Also fix zone map priority so local zones override RFC 6762 .local
special-use handling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib.rs

@@ -5,6 +5,7 @@ pub mod cache;
 pub mod config;
 pub mod ctx;
 pub mod dnssec;
+pub mod doh;
 pub mod dot;
 pub mod forward;
 pub mod header;