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-vt/build.rs

@@ -0,0 +1,37 @@
+//! Generates the sorted, lowercase X11 color table (`x11_table.rs`) from
+//! `src/res/rgb.txt`, so name lookups need neither a lazily built map nor a
+//! lowercased copy of the query (Zig builds the same table at comptime, so
+//! looking up a color never allocates).
+
+use std::{collections::HashSet, env, fmt::Write as _, fs, path::PathBuf};
+
+fn main() {
+    println!("cargo:rerun-if-changed=src/res/rgb.txt");
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let data = fs::read_to_string("src/res/rgb.txt").expect("read rgb.txt");
+    let mut seen = HashSet::new();
+    let mut entries: Vec<(String, u8, u8, u8)> = Vec::new();
+    for line in data.split('\n').filter(|l| !l.is_empty()) {
+        let comp = |r: std::ops::Range<usize>| -> u8 {
+            line[r].trim_matches(' ').parse().expect("bad rgb.txt")
+        };
+        let (r, g, b) = (comp(0..3), comp(4..7), comp(8..11));
+        let name = line[12..]
+            .trim_matches(|c| c == ' ' || c == '\t' || c == '\n')
+            .to_ascii_lowercase();
+        // The first spelling of a (case-insensitive) name wins.
+        if seen.insert(name.clone()) {
+            entries.push((name, r, g, b));
+        }
+    }
+    entries.sort_by(|a, b| a.0.as_bytes().cmp(b.0.as_bytes()));
+
+    let mut out = String::from("&[\n");
+    for (name, r, g, b) in &entries {
+        writeln!(out, "    ({name:?}, {r}, {g}, {b}),").expect("write");
+    }
+    out.push_str("]\n");
+    let dest = PathBuf::from(env::var("OUT_DIR").expect("OUT_DIR")).join("x11_table.rs");
+    fs::write(dest, out).expect("write x11_table.rs");
+}