refactor: purge Node.js, Rust is the one true backend

- Moved boosapi-rs/* to repo root
- Deleted all Node.js source (src/server/, src/web/, scripts/)
- Deleted node_modules, package.json, tsconfig, vite.config
- Updated .gitignore and AGENTS.md for Rust-only stack
- Fixed static file path for frontend dist/web/
- Dockerfile stays the same (already Rust-only)
- Kept dist/web/ for Rust static serving

src/routes/health.rs

@@ -0,0 +1,14 @@
+use crate::{error::AppResult, AppState};
+use axum::{extract::State, Json};
+use serde_json::{json, Value};
+
+pub async fn health_check(State(state): State<AppState>) -> AppResult<Json<Value>> {
+    // Simple DB ping
+    sqlx::query("SELECT 1").execute(&*state.db).await?;
+
+    Ok(Json(json!({
+        "status": "ok",
+        "database": "ok",
+        "version": env!("CARGO_PKG_VERSION"),
+    })))
+}