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-lib/src/main_c.rs

@@ -21,9 +21,15 @@ static ARGS: OnceLock<Vec<String>> = OnceLock::new();
 /// Build the `ghostty_string_s` for an owned string (Zig:
 /// `String.fromSlice` of an allocated `[:0]const u8`). Free with
 /// `ghostty_string_free`.
+#[cfg(test)]
 pub(crate) fn string_from_owned(s: &str) -> ghostty_string_s {
+    string_from_bytes(s.as_bytes())
+}
+
+/// [`string_from_owned`] for raw bytes (paths need not be UTF-8).
+pub(crate) fn string_from_bytes(s: &[u8]) -> ghostty_string_s {
     let mut bytes = Vec::with_capacity(s.len() + 1);
-    bytes.extend_from_slice(s.as_bytes());
+    bytes.extend_from_slice(s);
     bytes.push(0);
     let boxed = bytes.into_boxed_slice();
     let len = boxed.len() - 1;