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-core/src/surface/mod.rs

@@ -469,8 +469,8 @@ impl Surface {
                 .working_directory
                 .as_ref()
                 .and_then(|wd| wd.value())
-                .map(str::to_owned);
-            ecfg.resources_dir = global::state().resources_dir.host().map(str::to_owned);
+                .cloned();
+            ecfg.resources_dir = global::state().resources_dir.host().cloned();
             // The Windows exec backend has no pre-exec/post-fork hooks,
             // cgroup scopes or rlimits (Zig: Linux/POSIX only).
             #[cfg(unix)]
@@ -940,9 +940,8 @@ impl Surface {
             }
 
             Message::PwdChange(w) => {
-                // Keep the OSC 7 bytes (see `Pwd`): non-UTF-8 bytes are
-                // carried with the reversible byte escape.
-                let pwd = ghostty_os::osbytes::bytes_to_config_string(w.slice());
+                // Keep the OSC 7 bytes (see `Pwd`).
+                let pwd = ghostty_os::osbytes::EncodedOs::from_bytes(w.slice());
                 self.perform(RtAction::Pwd(Pwd { pwd }));
             }
 
@@ -1368,10 +1367,10 @@ impl Surface {
     /// Returns the pwd of the terminal, if any. This is always copied
     /// because the pwd can change at any point from termio.
     #[must_use]
-    pub fn pwd(&self) -> Option<String> {
+    pub fn pwd(&self) -> Option<ghostty_os::osbytes::EncodedOs> {
         let t = self.lock_terminal();
         let pwd = t.get_pwd()?;
-        Some(ghostty_os::osbytes::bytes_to_config_string(pwd))
+        Some(ghostty_os::osbytes::EncodedOs::from_bytes(pwd))
     }
 
     /// The raw bytes of [`Surface::pwd`] (Zig returns the OSC 7 bytes as is).