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, 49 insertions, 0 deletions

diff --git a/test/macos-snapshots/font.snap b/test/macos-snapshots/font.snap
new file mode 100644
index 00000000..71049b55
--- /dev/null
+++ b/test/macos-snapshots/font.snap
@@ -0,0 +1,49 @@
+# The font picker and the zoom, which are the two things this shell decides
+# entirely on its own. Neither is visible in a cell buffer — the core has no
+# font and no idea what a point is — so what a snapshot CAN see is the second
+# effect of both: a cell that changed size fits a different number of columns
+# into the same window, and the core reflows to it.
+#
+# `font` asserts the face by PostScript name, which is the only direct look at
+# the thing under test.
+start 24 100
+wait 8000 $
+stable 700 20000
+snap boot
+
+# Menlo ships with every macOS and ships inside a .ttc, so this is also the
+# end-to-end proof of the collection branch in src/fonts.zig: the core walks
+# the font directories, matches the name, hands over a path, and the host has
+# to pull face 0 out of a file holding four.
+command Font Menlo
+stable 700 20000
+font Menlo-Regular
+snap menlo
+
+# A name that resolves to nothing must leave the screen alone rather than
+# fall back to something. `Font` finds no file, sets no path, and the host is
+# never asked to do anything at all.
+command Font NoSuchFaceExistsHere
+stable 700 20000
+font Menlo-Regular
+snap unchanged
+
+# Zoom is a pure host property: no builtin, no core round trip, just a bigger
+# cell and the reflow that follows it. Four points is enough to move the grid
+# at any starting size.
+zoom 4
+stable 700 20000
+font Menlo-Regular
+snap bigger
+
+# ...and back, which must land on exactly the grid it started from — the whole
+# point of "actual size" being a fixed number rather than an undo stack.
+zoom reset
+stable 700 20000
+snap reset
+
+# Small enough to be worth checking the clamp does not run away: the range
+# floor is 6pt, so this asks for far past it and must simply stop.
+zoom -40
+stable 700 20000
+snap floor