feat: WASM web app (browser LesS/KEY) backed by the hel core

Run the real hel core in the browser via WebAssembly, replacing the plain-JS
ooke.github.io/sk reimplementation so the web and the CLI share one generator.

- hel core: new storage module (native fs / wasm localStorage) backs
  init/source/dump/correct; the pipe and pb branches are gated out of wasm;
  the wasm editor is completed (EditorRef) and its password prompt no longer
  blocks the single JS thread (synchronous hel_get_password instead of a
  thread::sleep poll).
- helwasm: hel_load_script for bulk import, a panic hook in hel_init, dropped
  the ok_add / web-sys leftovers; build.sh runs wasm-bindgen into a committed
  pkg/ so GitHub Pages can serve the static dir with no CI.
- UI: rewritten index.html + style.css in the kaizenkodo.org style — responsive,
  masked-but-copyable passwords with click-to-reveal, a quick-generate card plus
  a full command console, localStorage persistence, and paste import/export.

helwasm/src/lib.rs

@@ -4,13 +4,11 @@ extern crate hel;
 
 use wasm_bindgen::prelude::*;
 
-#[wasm_bindgen]
-pub fn ok_add(a: i32, b: i32) -> i32 {
-    a + b + 1
-}
-
 mod hel_state;
 
+/// Call once at page load: routes Rust panics to the browser console with a
+/// readable message + stack instead of an opaque "unreachable" trap.
 #[wasm_bindgen]
 pub fn hel_init() {
+    console_error_panic_hook::set_once();
 }