refactor: type escaped OS strings and fix the final audit findings

Escaped config strings (ghostty_os::osbytes) kept reaching OS
boundaries undecoded, and decoding was occasionally applied to plain
text. The root cause was that both were plain `String`s. Now:
- `EncodedOs` is a newtype (no Display/AsRef<Path>) that decodes only
  via to_os/to_path/to_bytes/to_wide; plain text enters via
  from_plain_text. OS helpers (env, home, xdg, passwd, resources dir,
  path expansion), config::Path, WorkingDirectory, theme/file_load/edit
  paths, terminal pwd, OpenUrl/Pwd actions and termio cwd use it, so the
  compiler forces decoding at every boundary. os::open takes &OsStr.
  Config output is unchanged.

Fixes all rows of docs/rewrite/notes/review-rv5-codex.md (final-Z7.md):
screen-file copy; regex/OSC 8 URLs no longer decoded (regression);
lossless Windows WTF-8/WTF-16 for args, env and CreateProcessW; Windows
resources dir/TERMINFO; color OSC request lists and X11 color lookup no
longer allocate globally (C zero-allocation test extended); macOS Mach
handler resumes all threads before KERN_FAILURE (hang regression) and
SIGABRT minidumps go through the exception thread; plus open-config,
background images, crash dir, ssh cache, exe dir/PATH, fontconfig
filenames, file links, kitty TMPDIR, .hushlogin and benchmark paths.
The typing also surfaced and fixed gtk-custom-css, bell audio, bash
HISTFILE, OSC 52 writes and the C config getters.

Test Plan:
- cargo test --workspace (3376 passed)
- just check-macos (both), just check-windows, just check-wasm
- diff <(ghostty-rs +show-config --default --docs) \
  <(ghostty +show-config --default --docs)

crates/ghostty-font/src/face/freetype.rs

@@ -131,11 +131,13 @@ impl Face {
     /// Initialize a new font face from a file.
     pub fn init_file(
         lib: &Library,
-        path: &str,
+        path: impl AsRef<std::path::Path>,
         index: i32,
         opts: Options,
     ) -> Result<Face, FaceError> {
-        let cpath = CString::new(path).map_err(|_| FaceError::InvalidPath)?;
+        // File names are raw OS bytes (they need not be UTF-8).
+        let cpath = CString::new(path.as_ref().as_os_str().as_encoded_bytes())
+            .map_err(|_| FaceError::InvalidPath)?;
         let face = {
             let _g = lib.lock();
             ft::FtFace::new_file(&lib.inner.lib, &cpath, index).map_err(FaceError::Freetype)?