enhance: wire up GEGL image filters (a cycle / s save) + fix export bugs

The enhancer module existed (GEGL presets: Auto-fix, Brightness, Contrast,
Saturation, Warm, Cool, Sharpen, Denoise) but was never connected to the
app and GEGL was never initialized. Wire it up:

- app.c: gegl_init() once in GApplication::startup (GEGL-gated).
- enhancer.c: add enhancer_load(GFile) -> GeglBuffer (gegl:load) and
  enhancer_buffer_to_texture(GeglBuffer) -> GdkTexture (RGBA8 ->
  GdkMemoryTexture) for the live preview bridge.
- enhancer_export: pick the saver from the output extension (jpg/png/webp)
  instead of always gegl:jpg-save (ju0 - was writing JPEG bytes into .png);
  verify the save actually produced a non-empty newer file instead of
  trusting g_file_test(EXISTS) on a pre-existing path (ku0 - false success).
- window.c: win.enhance (a) cycles the active preset and previews it on the
  current image (switches to large view, loads via GEGL, applies, shows the
  texture); win.enhance-save (s) exports <stem>-enhanced.<ext> with the
  active preset, never overwriting the original. Preview resets on
  navigation; the title shows the active preset.
- shortcuts.c: a -> win.enhance, s -> win.enhance-save; ? overlay Enhance
  group.
- tests: test_enhancer gains load_and_to_texture, export_format (PNG/JPEG
  signature checks), export_real_success (ku0 - parent-missing and
  pre-existing-directory both return FALSE). LSAN suppressions cover
  GEGL's jpg-load plugin leak. test_shortcut full-table updated (25 rows).

Synchronous apply (may briefly block on large images) and a navigate-away
dirty prompt are deliberately out of scope for v1.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/enhancer.h b/src/enhancer.h
index fce3fe7..f466d21 100644
--- a/src/enhancer.h
+++ b/src/enhancer.h
@@ -1,6 +1,9 @@
 #ifndef GGAZE_ENHANCER_H
 #define GGAZE_ENHANCER_H
 
+#include "ggaze-config.h"
+
+#include <gdk/gdk.h>
 #include <gio/gio.h>
 #include <glib.h>
 #include <gegl.h>
@@ -25,12 +28,25 @@ const GPtrArray *enhancer_get_presets(Enhancer *p_e);
 GeglBuffer *enhancer_apply(Enhancer *p_e, GeglBuffer *p_in,
                            const EnhancerPreset *p_preset, GError **p_err);
 
-/* Export the enhanced buffer to a file (JPEG quality 95, EXIF Orientation=1).
- * Returns TRUE on success. */
+/* Export the enhanced buffer to a file. The saver is chosen from p_out's
+ * extension: .jpg/.jpeg -> gegl:jpg-save (quality 95), .png -> gegl:png-save,
+ * .webp -> gegl:webp-save (if available). Other extensions fail with
+ * G_IO_ERROR_NOT_SUPPORTED. Success is verified by a real stat of the output
+ * (not pre-existence). Returns TRUE on success. */
 gboolean enhancer_export(Enhancer *p_e, GeglBuffer *p_in,
                          const EnhancerPreset *p_preset, GFile *p_out,
                          GError **p_err);
 
+#if GGAZE_HAVE_GEGL
+/* Load a file into a GeglBuffer via the gegl:load op. Returns a new buffer
+ * (caller unrefs) or NULL with p_err set. */
+GeglBuffer *enhancer_load(GFile *p_file, GError **p_err);
+
+/* Convert a GeglBuffer to a GdkTexture for preview (RGBA8 bytes). Returns a
+ * new GdkTexture (caller unrefs) or NULL with p_err set. Needs no display. */
+GdkTexture *enhancer_buffer_to_texture(GeglBuffer *p_buf, GError **p_err);
+#endif /* GGAZE_HAVE_GEGL */
+
 G_END_DECLS
 
 #endif
\ No newline at end of file