feat: HTTP protocol plugin + XDP globals patching from config

protocol-http (compile-time feature):
- HttpHandler: incremental HTTP/1.1 request parse (fragment-safe),
  header size/timeout limits, method whitelist, Host required,
  blocked_paths, optional User-Agent requirement
- [protocol.http] config section; registry wiring behind feature

XDP globals:
- src/xdp/globals.rs: XdpGlobals + build_rodata_image() mirroring
  xdp/core/config.h layout; set via OpenMapMut::set_initial_value()
  before load ([xdp] section: ports, udp policy, throttle, challenge)
- wire set_globals into rampart binary startup

fix: gate preflight() behind xdp feature (dead code without it)

Cargo.toml

@@ -37,8 +37,8 @@ store-redis = ["dep:redis"]
 geoip = ["dep:maxminddb"]
 xdp = ["dep:libbpf-rs", "dep:libc"]
 io-uring = ["dep:tokio-splice"]
-# Резерв под реализацию HTTP-протокольного обработчика (модель plugin-by-feature).
-# Реализаций пока нет: реестр протоколов пуст и edge-нода требует явного флага.
+# HTTP/1.1 protocol handler: парсинг request-head, verdict Allow/Reject,
+# туннелирование на upstream (см. src/protocol/http/ и [protocol.http] в конфиге).
 protocol-http = []
 
 [dependencies]