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-renderer/src/shadertoy.rs

@@ -80,9 +80,9 @@ pub enum Target {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum PathItem {
     /// A path that may be missing (`?path`); missing files are skipped.
-    Optional(String),
+    Optional(std::path::PathBuf),
     /// A path that must exist.
-    Required(String),
+    Required(std::path::PathBuf),
 }
 
 #[derive(Debug, thiserror::Error)]
@@ -124,14 +124,14 @@ pub fn load_from_files(paths: &[PathItem], target: Target) -> Result<Vec<String>
             PathItem::Required(p) => (p, false),
         };
 
-        let shader = match load_from_file(&ghostty_os::osbytes::config_str_to_path(path), target) {
+        let shader = match load_from_file(path, target) {
             Ok(s) => s,
             Err(Error::Io(e)) if optional && e.kind() == std::io::ErrorKind::NotFound => {
                 continue;
             }
             Err(e) => return Err(e),
         };
-        log::info!("loaded custom shader path={path}");
+        log::info!("loaded custom shader path={}", path.display());
         list.push(shader);
     }
 
@@ -709,13 +709,13 @@ mod tests {
         let missing = dir.join("missing.glsl");
 
         let items = [
-            PathItem::Optional(missing.to_string_lossy().into_owned()),
-            PathItem::Required(good.to_string_lossy().into_owned()),
+            PathItem::Optional(missing.clone()),
+            PathItem::Required(good.clone()),
         ];
         let shaders = load_from_files(&items, Target::Glsl).unwrap();
         assert_eq!(shaders.len(), 1);
 
-        let items = [PathItem::Required(missing.to_string_lossy().into_owned())];
+        let items = [PathItem::Required(missing.clone())];
         assert!(matches!(
             load_from_files(&items, Target::Glsl),
             Err(Error::Io(_))