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/tests/node.rs

@@ -1,14 +1,32 @@
 //! Builds the wasm module and runs `tests/node_test.js` against it with
-//! node, using stub JS imports (a fake canvas measuring API). Skipped when
+//! node, with zig-js's own JS host and a fake `document`/canvas. Skipped when
 //! node or the `wasm32-unknown-unknown` target is not available.
 
 use std::{path::PathBuf, process::Command};
 
 #[test]
 fn wasm_module_runs_under_node() {
-    if Command::new("node").arg("--version").output().is_err() {
+    // zig-js's host is TypeScript; node must be able to strip types (>= 23.6).
+    let Some(major) = Command::new("node")
+        .arg("--version")
+        .output()
+        .ok()
+        .and_then(|o| {
+            String::from_utf8_lossy(&o.stdout)
+                .trim()
+                .trim_start_matches('v')
+                .split('.')
+                .next()?
+                .parse::<u32>()
+                .ok()
+        })
+    else {
         eprintln!("skipping: node not found");
         return;
+    };
+    if major < 24 {
+        eprintln!("skipping: node {major} cannot load the zig-js TypeScript host");
+        return;
     }
 
     let manifest = PathBuf::from(env!("CARGO_MANIFEST_DIR"));