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-termio/src/stream_handler.rs

@@ -1022,7 +1022,7 @@ impl StreamHandler<'_> {
         Ok(())
     }
 
-    fn color_operation(&mut self, requests: &osc_color::List, terminator: Terminator) {
+    fn color_operation(&mut self, requests: &osc_color::List<'_>, terminator: Terminator) {
         // return early if there is nothing to do
         if requests.is_empty() {
             return;
@@ -1030,8 +1030,8 @@ impl StreamHandler<'_> {
 
         let mut response: Vec<u8> = Vec::new();
 
-        for req in requests {
-            match *req {
+        for req in requests.iter() {
+            match req {
                 Request::Set(set) => {
                     match set.target {
                         Target::Palette(i) => {
@@ -1216,13 +1216,13 @@ impl StreamHandler<'_> {
         }
     }
 
-    fn kitty_color_report(&mut self, request: &kitty::color::OSC) {
+    fn kitty_color_report(&mut self, request: &kitty::color::OSC<'_>) {
         use kitty::color::{Kind, Request as KReq, Special};
 
         let mut out: Vec<u8> = Vec::new();
 
-        for item in &request.list {
-            match item {
+        for item in request.list.iter() {
+            match &item {
                 KReq::Query(key) => {
                     // If the writer buffer is empty, we need to write our prefix
                     if out.is_empty() {