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/build.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+# Build the helwasm web bundle into helwasm/pkg/ (committed so GitHub Pages can
+# serve the static dir directly, no CI). Requires the wasm32 target and a
+# wasm-bindgen CLI matching the wasm-bindgen crate version:
+#   rustup target add wasm32-unknown-unknown
+#   cargo install wasm-bindgen-cli --version <crate version>
+set -e
+cd "$(dirname "$0")/.."
+cargo build --target wasm32-unknown-unknown -p helwasm --release
+wasm-bindgen --target web --out-dir helwasm/pkg \
+  target/wasm32-unknown-unknown/release/helwasm.wasm
+echo "built helwasm/pkg/ (helwasm.js + helwasm_bg.wasm)"