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)