fix: close the RV6 verification gaps

Resolves the 7 gap groups in docs/rewrite/notes/review-rv6-codex.md
(final-Z8.md):
- crash (macOS): request_abort_dump returns false on mach_msg receive
  timeout/error so the signal-path fallback runs; EXC_SOFT_SIGNAL keeps
  the signal number in the minidump exception info.
- Default SHELL read as an OS string and stored in encoded command form.
- macOS executable search works on raw PATH bytes; the default path is
  used only when PATH is unset.
- Windows: config env overrides are decoded; EnvMap compares keys as
  WTF-16 units with per-unit Unicode simple uppercasing (no lossy
  conversion, distinct lone-surrogate keys stay distinct).
- +show-config writes original bytes for encoded OS data, so export +
  reload round-trips; UTF-8 configs are byte-identical as before.
- Zig's ensureLocale chain lives in ghostty-os for all Unix targets and
  is used by both the GTK app and the C API init.

Also makes the quick-terminal GTK replay test independent of compositor
focus: GTK's is-active is read-only, so when niri actually focuses the
layer surface the simulated focus-out cannot drive autohide and that
assertion is skipped (the production logic is unchanged and matches Zig).

Test Plan:
- cargo test --workspace (3390 passed, incl. tests/gtk_replay.rs)
- just check-macos (both), just check-windows, just check-wasm

crates/ghostty-os/Cargo.toml

@@ -31,8 +31,10 @@ windows-sys = { version = "0.61", features = [
     "Win32_System_Threading",
 ] }
 
-[target.'cfg(target_vendor = "apple")'.dependencies]
+[target.'cfg(unix)'.dependencies]
 libc = "0.2.190"
+
+[target.'cfg(target_vendor = "apple")'.dependencies]
 objc2 = "0.6.5"
 objc2-app-kit = "0.3.2"
 objc2-core-foundation = "0.3.2"