merge the macOS app branch: the AppKit shell, pixel attachments, live theming, and mupdf -Djpx

Three commits off 38e9919 (macos-app@upstream) merged into main's ghostty bump.
No textual conflicts, and two things the merge needed:

- nested.zig asked libc for fstatat. Darwin has it; on linux std.c declares it
  `void` (glibc hides it behind a versioned symbol std cannot name), so the tty
  build stopped at 'type void not a function'. statNoFollow keeps fstatat on
  darwin and asks statx on linux for the same three fields, which is what this
  file did before the branch generalized it to both platforms.

- .DS_Store rode along with a797a1a. Deleted, and .gitignore now says so.

linux: snap 86/86, unit-test, image-harness and mupdf-check green. nested.zig
also type-checks for aarch64-macos.

1 files changed, 32 insertions, 0 deletions

diff --git a/test/macos-snapshots/cwd.snap b/test/macos-snapshots/cwd.snap
new file mode 100644
index 00000000..87f6f9ef
--- /dev/null
+++ b/test/macos-snapshots/cwd.snap
@@ -0,0 +1,32 @@
+# The pane tag has to follow the shell around, because a relative `Look` is
+# resolved against it: with a stale cwd, clicking `README.md` after a `cd`
+# looks for it in the directory the pane was SPAWNED in and finds nothing.
+#
+# On linux the host re-reads /proc/<pid>/cwd every frame. macOS asks libproc,
+# and asks it only for a pane that just produced output — a `cd` is a command
+# and a shell that ran a command prints its next prompt, so nothing else can
+# have moved one. This script is what proves that gating is not too clever:
+# the tag must be right AFTER the cd and must stay right when nothing happens.
+start 24 100
+wait 8000 $
+stable 700 20000
+# The hermetic world puts the shell in <base>/work, so the boot tag names it
+# and no absolute path from this machine can leak into the golden.
+snap spawned
+# `cd` writes nothing but the next prompt: the one and only signal the lazy
+# refresh gets. Two of them, because the second has to survive the first
+# having already cleared the flag.
+text cd /tmp
+key enter
+wait 8000 $
+stable 700 20000
+snap moved
+text cd /
+key enter
+wait 8000 $
+stable 700 20000
+snap moved-again
+# ...and an idle pass must not lose it again: the refresh clears its own flag,
+# so a tick with no output must leave the tag exactly where it was.
+stable 700 20000
+snap idle