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-core/src/surface/clipboard.rs

@@ -64,7 +64,8 @@ impl Surface {
             log::info!("application sent invalid base64 data for OSC 52");
             return;
         };
-        let text = String::from_utf8_lossy(&decoded).into_owned();
+        // OSC 52 data is written as the application sent it (bytes).
+        let text = decoded;
 
         // When clipboard-write is "ask" a prompt is displayed to the user
         // asking them to confirm the clipboard access. Each app runtime
@@ -111,11 +112,11 @@ impl Surface {
             }
         };
 
-        let mut contents: Vec<(String, String)> = Vec::new();
+        let mut contents: Vec<(String, Vec<u8>)> = Vec::new();
         match format {
             CopyToClipboard::Plain => {
                 let Some(s) = run(opts) else { return };
-                contents.push(("text/plain".to_owned(), s));
+                contents.push(("text/plain".to_owned(), s.into_bytes()));
             }
 
             CopyToClipboard::Vt => {
@@ -125,7 +126,7 @@ impl Surface {
                 // it contains escape sequences that should be preserved
                 // as-is
                 let Some(s) = run(o) else { return };
-                contents.push(("text/plain".to_owned(), s));
+                contents.push(("text/plain".to_owned(), s.into_bytes()));
             }
 
             CopyToClipboard::Html => {
@@ -135,7 +136,7 @@ impl Surface {
                 // since HTML has its own character encoding and entity
                 // system
                 let Some(s) = run(o) else { return };
-                contents.push(("text/html".to_owned(), s));
+                contents.push(("text/html".to_owned(), s.into_bytes()));
             }
 
             CopyToClipboard::Mixed => {
@@ -143,7 +144,7 @@ impl Surface {
                 let Some(plain) = run(opts.clone()) else {
                     return;
                 };
-                contents.push(("text/plain".to_owned(), plain));
+                contents.push(("text/plain".to_owned(), plain.into_bytes()));
 
                 // Second, generate HTML without codepoint mappings
                 let mut o = opts;
@@ -154,7 +155,7 @@ impl Surface {
                 o.background = None;
                 o.foreground = None;
                 let Some(html) = run(o) else { return };
-                contents.push(("text/html".to_owned(), html));
+                contents.push(("text/html".to_owned(), html.into_bytes()));
             }
         }
 
@@ -207,7 +208,7 @@ impl Surface {
             ClipboardRequest::Osc52Write(clipboard) => {
                 self.rt_surface.set_clipboard(
                     clipboard,
-                    &[("text/plain".to_owned(), data.to_owned())],
+                    &[("text/plain".to_owned(), data.as_bytes().to_vec())],
                     !confirmed,
                 );
                 Ok(())