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-cli/src/new_window.rs

@@ -8,6 +8,7 @@ use std::sync::OnceLock;
 
 use ghostty_apprt::ipc;
 use ghostty_config::cli_args::{ArgError, ArgIter, CliTarget};
+use ghostty_os::osbytes::EncodedOs;
 
 use crate::error::Error;
 
@@ -56,15 +57,15 @@ impl Options {
             if stripped == "home" || stripped == "inherit" {
                 return Ok(Some(arg.to_string()));
             }
-            let expanded =
-                ghostty_os::expand_home(stripped).map_err(|e| ArgError::Other(e.to_string()))?;
-            let realpath =
-                std::fs::canonicalize(ghostty_os::osbytes::config_str_to_path(&expanded))
-                    .map_err(|e| ArgError::Other(e.to_string()))?;
+            // The CLI argument is an encoded OS string.
+            let expanded = ghostty_os::expand_home(&EncodedOs::from_encoded(stripped))
+                .map_err(|e| ArgError::Other(e.to_string()))?;
+            let realpath = std::fs::canonicalize(expanded.to_path())
+                .map_err(|e| ArgError::Other(e.to_string()))?;
             self.working_directory_seen = true;
             return Ok(Some(format!(
                 "--working-directory={}",
-                ghostty_os::osbytes::path_to_config_string(&realpath)
+                EncodedOs::from_path(&realpath).as_encoded()
             )));
         }