destroy --purge: also wipe agent state dirs

new --purge flag on the destroy verb (cli + admin socket + dashboard).
default destroy still keeps /var/lib/hyperhive/{agents,applied}/<name>/
so recreating with the same name reuses prior config + creds.
with --purge, both dirs go too (config history, claude creds, /state/
notes). no undo. dashboard adds a separate PURG3 button with an
explicit confirmation copy; the existing DESTR0Y button keeps the
soft semantics.

claude.md dashboard-action-surface section updated; todo entry
dropped.

hive-c0re/src/dashboard.rs

@@ -424,8 +424,20 @@ fn strip_container_prefix(name: &str) -> String {
         .to_owned()
 }
 
-async fn post_destroy(State(state): State<AppState>, AxumPath(name): AxumPath<String>) -> Response {
-    match actions::destroy(&state.coord, &name).await {
+#[derive(Deserialize, Default)]
+struct DestroyForm {
+    #[serde(default)]
+    purge: Option<String>,
+}
+
+async fn post_destroy(
+    State(state): State<AppState>,
+    AxumPath(name): AxumPath<String>,
+    Form(form): Form<DestroyForm>,
+) -> Response {
+    // Checkbox semantics: any non-empty value (axum sends "on") = purge.
+    let purge = form.purge.as_deref().is_some_and(|v| !v.is_empty());
+    match actions::destroy(&state.coord, &name, purge).await {
         Ok(()) => Redirect::to("/").into_response(),
         Err(e) => error_response(&format!("destroy {name} failed: {e:#}")),
     }