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-crash/src/sentry.rs

@@ -138,7 +138,8 @@ pub fn install(opts: &Options) -> Result<(), InitError> {
     }
 
     let state = State {
-        dir: dir.as_os_str().as_encoded_bytes().to_vec(),
+        // Bytes on Unix, WTF-8 on Windows (lossless both ways).
+        dir: ghostty_os::osbytes::os_bytes(dir.as_os_str()),
         prefix,
     };
     if STATE.set(state).is_err() {
@@ -415,17 +416,8 @@ pub(crate) fn write_report_ext(
         data.extend_from_slice(&enc.payload);
     }
 
-    #[cfg(unix)]
-    let dir = {
-        use std::os::unix::ffi::OsStrExt as _;
-        std::path::Path::new(std::ffi::OsStr::from_bytes(&st.dir))
-    };
-    // Windows paths are not arbitrary bytes; the dir was UTF-8 in practice.
-    #[cfg(not(unix))]
-    let dir_buf = PathBuf::from(String::from_utf8_lossy(&st.dir).into_owned());
-    #[cfg(not(unix))]
-    let dir = dir_buf.as_path();
-    std::fs::create_dir_all(dir)?;
+    let dir = PathBuf::from(ghostty_os::osbytes::os_from_bytes(st.dir.clone()));
+    std::fs::create_dir_all(&dir)?;
     let path = dir.join(report_file_name(uuid));
     std::fs::write(&path, data)?;
     Ok(path)