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.

hel/src/storage.rs

@@ -0,0 +1,48 @@
+//! Key -> value persistence with a per-target backend.
+//!
+//! - Native: the key is a filesystem path; backed by `std::fs`.
+//! - WASM: the key is a localStorage key; backed by JS imports
+//!   `hel_storage_get` / `hel_storage_set` (provided by the host page).
+//!
+//! This lets the same command code (`init`, `source`, `dump`/`save`, `correct`)
+//! persist to files on the CLI and to the browser's localStorage on the web,
+//! with no per-call-site branching.
+
+use std::io;
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn read(key: &str) -> io::Result<String> {
+    std::fs::read_to_string(key)
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn write(key: &str, data: &str) -> io::Result<()> {
+    std::fs::write(key, data)
+}
+
+#[cfg(target_arch = "wasm32")]
+mod imp {
+    use wasm_bindgen::prelude::*;
+
+    #[wasm_bindgen]
+    extern "C" {
+        #[wasm_bindgen(js_name = hel_storage_get)]
+        pub fn get(key: &str) -> Option<String>;
+        #[wasm_bindgen(js_name = hel_storage_set)]
+        pub fn set(key: &str, val: &str);
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+pub fn read(key: &str) -> io::Result<String> {
+    match imp::get(key) {
+        Some(v) => Ok(v),
+        None => Err(io::Error::new(io::ErrorKind::NotFound, "key not found in localStorage")),
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+pub fn write(key: &str, data: &str) -> io::Result<()> {
+    imp::set(key, data);
+    Ok(())
+}