feat!: universal redesign — drop Minecraft stack, single-crate architecture

- remove Java plugins (velocity/paper), dashboard, all MC-specific code
  (handshake, death_code, varint, hostname-HMAC); available in history pre-v0.2
- merge crates/* into one package with src/bin/{rampart,rampart-manager,rampart-cli}
- ProtocolHandler trait + registry (no implementations yet), universal PoW kept
- XDP: universal L3/L4 filter (xdp/core/) + pluggable hook API (xdp/hooks/),
  fix IPv6 saddr bug; clang build verified
- docs: bilingual knowledge base (docs/kb/: attacks x4, defense-levels,
  practice x3), rewrite README/architecture for universal concept
- TODO.md v4.0: <=300-line module limit, competitor benchmark section (ref/)
- deploy/CI/docs cleanup: no MC references, new binary names

cargo build/clippy(-D warnings)/test green (55 tests)

src/manager/api/health.rs

@@ -0,0 +1,18 @@
+use crate::manager::AppState;
+use axum::Json;
+use axum::extract::State;
+use serde::Serialize;
+use std::sync::Arc;
+
+#[derive(Serialize)]
+pub struct HealthResponse {
+    pub status: String,
+    pub version: String,
+}
+
+pub async fn health_check(State(_state): State<Arc<AppState>>) -> Json<HealthResponse> {
+    Json(HealthResponse {
+        status: "healthy".to_string(),
+        version: env!("CARGO_PKG_VERSION").to_string(),
+    })
+}