fullscreen: info/EXIF, fullscreen, slideshow, Esc back (ot0)

M4 (task ot0): fullscreen + slideshow + info overlay.

- src/info.{c,h}: plain-C EXIF gather via libexif (camera, lens, focal,
  aperture, shutter, ISO, datetime, orientation) + file info (dims, format,
  size). info_format() produces the overlay text. Unit-tested.
- src/window.c: fullscreen toggle (f), slideshow (S, 3s auto-advance), info
  overlay (i, GtkLabel in GtkOverlay, auto-hide 5s), Esc contextual back
  (fullscreen→unfullscreen→large→grid→quit). Stack wrapped in GtkOverlay.
  ggaze_window_get_stack() accessor for tests.
- src/shortcuts.c: f, S, i, Escape bindings.
- meson.build: libexif dep added.
- tests: unit test_info (EXIF extraction + orientation tag). 14/14 green,
  ASan clean.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/window.h b/src/window.h
index 10612db..43572d0 100644
--- a/src/window.h
+++ b/src/window.h
@@ -32,6 +32,10 @@ GgazeWindow *ggaze_window_new(GgazeApp *p_app);
  * current image into the viewer and switches the stack to "large". */
 void ggaze_window_open(GgazeWindow *p_win, GFile *p_arg);
 
+/* The GtkStack (grid/large) — the tests use this instead of
+ * gtk_window_get_child (which now returns the wrapping GtkOverlay). */
+GtkStack *ggaze_window_get_stack(GgazeWindow *p_win);
+
 /* Navigation over the current folder (bound to h/l/Left/Right/g/G via
  * shortcuts.c). No-ops if nothing is open. */
 void ggaze_window_prev(GgazeWindow *p_win);