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-apprt/src/surface.rs

@@ -222,7 +222,11 @@ pub fn should_inherit_working_directory(context: NewSurfaceContext, config: &Con
 /// `app.focusedSurface()?.pwd()`), which the caller (core) must look up.
 // TODO(integration): core could wrap this to resolve the focused surface.
 #[must_use]
-pub fn new_config(config: &Config, context: NewSurfaceContext, prev_pwd: Option<String>) -> Config {
+pub fn new_config(
+    config: &Config,
+    context: NewSurfaceContext,
+    prev_pwd: Option<ghostty_os::osbytes::EncodedOs>,
+) -> Config {
     let mut copy = config.clone();
     if let Some(pwd) = prev_pwd
         && should_inherit_working_directory(context, config)
@@ -238,6 +242,10 @@ mod tests {
 
     use super::*;
 
+    fn tmp() -> ghostty_os::osbytes::EncodedOs {
+        ghostty_os::osbytes::EncodedOs::from_encoded("/tmp")
+    }
+
     struct Rec(RefCell<Vec<(u32, bool)>>);
     impl AppMailbox<u32> for Rec {
         fn push_surface_message(&self, s: u32, m: Message, _t: Timeout) -> usize {
@@ -277,12 +285,9 @@ mod tests {
             NewSurfaceContext::Tab,
             &c
         ));
-        let n = new_config(&c, NewSurfaceContext::Window, Some("/tmp".into()));
-        assert_eq!(
-            n.working_directory,
-            Some(WorkingDirectory::Path("/tmp".into()))
-        );
-        let n = new_config(&c, NewSurfaceContext::Tab, Some("/tmp".into()));
+        let n = new_config(&c, NewSurfaceContext::Window, Some(tmp()));
+        assert_eq!(n.working_directory, Some(WorkingDirectory::Path(tmp())));
+        let n = new_config(&c, NewSurfaceContext::Tab, Some(tmp()));
         assert_eq!(n.working_directory, None);
     }
 }