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/src/face.rs

@@ -53,7 +53,10 @@ pub extern "C" fn face_new(ptr: *const u8, len: usize, pts: u16, p: u16) -> *mut
     };
     match Face::init_named(raw, DesiredSize::new(f32::from(pts)), p) {
         Ok(face) => Box::into_raw(Box::new(face)),
-        Err(_) => std::ptr::null_mut(),
+        Err(err) => {
+            log::warn!("error creating face err={err}");
+            std::ptr::null_mut()
+        }
     }
 }