macos: pixel attachments, live theming, and a signed app

The AppKit shell now draws what the core renders, follows the theme without a
relaunch, and builds into something you can hand to someone.

- Pixel attachments. Surface.images was dropped on the floor here, so a PDF
  pane showed nothing at all: native_images is now set, pardes_image_s carries
  the geometry the core already clipped, and PardesView keeps one CGImage per
  (serial, page, revision) so scrolling costs a draw and not a decode. Image
  panes get real pixels instead of the petscii fallback.

- Themes take hold live. pardes_tick never advanced the chrome animation, so
  every tagline kept the previous theme's colours until the next launch and
  the 16 ms re-pump spun for the rest of the session. pardes_theme_bg retires
  the hand-agreed #121212 and drives the window background and the titlebar
  appearance; a theme with no background of its own now gets a transparent
  window over an NSVisualEffectView.

- The cell snaps to whole DEVICE pixels rather than whole points. Monaco
  advances 8.4014pt at 14, so ceiling to 9 spaced every column 7.1% wider than
  the face was drawn for.

- The dial is one notch per 10 degrees instead of 20, and a release keeps
  turning in proportion to how hard it was thrown -- ramping up from zero at
  the floor, so a slow twist coasts not a little but not at all.

- A file dropped on the grid is a click plus Look, so it opens beside the pane
  it was dropped on. No drop concept was added to the core.

- The titlebar follows the focused pane: proxy icon, filename, and the dirty
  dot. File.saved_revision is the watermark that last one needed.

- Config (SPC f c) prints the resolved startup config path.

- build.zig assembles, signs and packages the bundle itself; build-app.sh is
  gone. -Dmacos-identity= takes a Developer ID, macos-dmg makes the image, and
  the icon is Glenda.

1 files changed, 7 insertions, 3 deletions

diff --git a/test/snapshots/builtins.snap b/test/snapshots/builtins.snap
index 93e33710..f6b5723b 100644
--- a/test/snapshots/builtins.snap
+++ b/test/snapshots/builtins.snap
@@ -49,12 +49,16 @@ stable 700 15000
 snap window-group
 # back to the whole index, and a NAME in it is live text like anywhere else:
 # middle-click `Tutor` and the tutor opens. That is the picking a stepping
-# picker would have done, minus running the thirty-nine rows you passed.
+# picker would have done, minus running the rows you passed.
+#
+# The one place in this suite a builtin cannot be added for free: the click is
+# a SCREEN coordinate, so every row inserted above `SPC h t` in the listing
+# moves Tutor down one and this number with it.
 key space ?
 wait 10000 SPC c n
 stable 700 15000
-press middle 20 45
-release middle 20 45
+press middle 20 46
+release middle 20 46
 wait 10000 PARDES TUTOR
 stable 700 15000
 snap tutor-from-index