feat(wasm): use zig-js's exact JS interop ABI

Ghostty's wasm code talks to JavaScript through the zig-js library
(mitchellh/zig-js, pinned in build.zig.zon). The first port invented its
own import ABI because the dependency wasn't available; now:
- ghostty-os/src/wasm/js.rs is a Rust port of zig-js's Zig side (Ref,
  Value, Object get/set/call/new, global, runtime, string) using its
  "zig-js" import module, function names and NaN-boxed value refs.
- web_canvas face and the atlas debug canvas make the same JS calls as
  Ghostty's Zig code.
- zig-js's unmodified JS host (+ LICENSE) is vendored under
  crates/ghostty-wasm/js/zig-js and drives the node test.

Test Plan:
- cargo test -p ghostty-wasm (node >= 24; asserts zig-js imports and no
  leaked host values)

crates/ghostty-wasm/js/zig-js/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "zig-js-glue",
+  "version": "0.1.3",
+  "description": "JS glue for Zig to interface with JS from Wasm",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/mitchellh/zig-js.git"
+  },
+  "source": "src/index.ts",
+  "main": "dist/index.js",
+  "module": "dist/module.js",
+  "types": "dist/types.d.ts",
+  "scripts": {
+    "prepare": "parcel build",
+    "build": "parcel build",
+    "test": "jest",
+    "check": "tsc --noEmit"
+  },
+  "author": "Mitchell Hashimoto",
+  "license": "MIT",
+  "devDependencies": {
+    "@parcel/packager-ts": "^2.8.0",
+    "@parcel/transformer-typescript-types": "^2.8.0",
+    "@types/jest": "^29.2.3",
+    "jest": "^29.3.1",
+    "parcel": "^2.8.0",
+    "ts-jest": "^29.0.3",
+    "typescript": "^4.9.3"
+  }
+}