feat(wasm): port Ghostty's wasm32 build

Ports main_wasm.zig as crates/ghostty-wasm (cdylib exporting the Zig
names: atlas_*, face_*, deferred_face_*, shaper_*, config_*), the
web_canvas font face and shaper (backend selected on wasm32), os/wasm
(logging, target, JS interop) and config/Wasm.zig.

C-library dependencies (freetype, harfbuzz, fontconfig, onig, gettext,
D-Bus, rustix) are target-gated. Like Zig's wasm build, link regex
search (StringMap::search_iterator) is unavailable without Oniguruma;
Collection/SharedGrid/harfbuzz are compiled out on wasm32. ghostty-os
switches from forbid to deny unsafe_code for the JS import blocks.

The JS import ABI is currently a documented handle-based interface with
a reference host (js/ghostty_host.js); aligning it with zig-js's exact
import names follows separately.

Test Plan:
- cargo build --target wasm32-unknown-unknown -p ghostty-font \
  -p ghostty-config -p ghostty-terminal -p ghostty-vt -p ghostty-wasm
- cargo test -p ghostty-wasm (node runs the module against a fake canvas)

crates/ghostty-config/src/config.rs

@@ -3976,7 +3976,18 @@ impl Config {
         //
         // See: https://github.com/Vladimir-csp/xdg-terminal-exec
         {
+            #[cfg(unix)]
             use std::os::unix::ffi::OsStrExt;
+            #[cfg(not(unix))]
+            trait OsStrExt {
+                fn as_bytes(&self) -> &[u8];
+            }
+            #[cfg(not(unix))]
+            impl OsStrExt for std::ffi::OsString {
+                fn as_bytes(&self) -> &[u8] {
+                    self.as_encoded_bytes()
+                }
+            }
             let cargs: Vec<std::ffi::CString> = argv
                 .iter()
                 .filter_map(|a| std::ffi::CString::new(a.as_bytes()).ok())
@@ -4619,22 +4630,13 @@ fn zig_io_error_name(err: &std::io::Error) -> String {
 }
 
 fn file_kind_name(meta: &std::fs::Metadata) -> &'static str {
-    use std::os::unix::fs::FileTypeExt;
     let ft = meta.file_type();
     if ft.is_dir() {
         "directory"
     } else if ft.is_symlink() {
         "sym_link"
-    } else if ft.is_block_device() {
-        "block_device"
-    } else if ft.is_char_device() {
-        "character_device"
-    } else if ft.is_fifo() {
-        "named_pipe"
-    } else if ft.is_socket() {
-        "unix_domain_socket"
     } else {
-        "unknown"
+        crate::theme::special_kind_name(ft)
     }
 }
 

crates/ghostty-config/src/theme.rs

@@ -94,14 +94,21 @@ fn diag(diags: &mut DiagnosticList, message: String) {
 }
 
 fn kind_name(ft: std::fs::FileType) -> &'static str {
-    use std::os::unix::fs::FileTypeExt;
     if ft.is_file() {
         "file"
     } else if ft.is_dir() {
         "directory"
     } else if ft.is_symlink() {
         "sym_link"
-    } else if ft.is_block_device() {
+    } else {
+        special_kind_name(ft)
+    }
+}
+
+#[cfg(unix)]
+pub(crate) fn special_kind_name(ft: std::fs::FileType) -> &'static str {
+    use std::os::unix::fs::FileTypeExt;
+    if ft.is_block_device() {
         "block_device"
     } else if ft.is_char_device() {
         "character_device"
@@ -114,6 +121,12 @@ fn kind_name(ft: std::fs::FileType) -> &'static str {
     }
 }
 
+/// wasm32 has no special file types (`std::os::unix` is unavailable).
+#[cfg(not(unix))]
+pub(crate) fn special_kind_name(_: std::fs::FileType) -> &'static str {
+    "unknown"
+}
+
 /// Verify that the file is a regular file, adding a diagnostic otherwise.
 fn check_regular(file: &File, theme: &str, diags: &mut DiagnosticList) -> bool {
     match file.metadata() {