Fix crop editor's drag/zoom math not matching its own preview

Reported: dragging toward an image edge (e.g. to reveal a cropped-off
head) stopped short of what the reference preview showed was possible —
the two panels visibly disagreed.

Root cause: transform-origin was set to match the pan position (X%,Y%)
instead of staying at the CSS default (50% 50%, the box's own center).
CSS object-position places the *unzoomed* crop; transform:scale then
magnifies around transform-origin. Tying that origin to X/Y meant zoom
dragged its own anchor point toward whichever edge you'd panned to,
instead of always magnifying what's actually centered in the frame —
harmless near the middle (why initial testing looked fine) but
increasingly wrong the closer you drag to an edge, exactly where you'd
need to go to reach a cropped head. A second, smaller error was in how
the reference-rectangle preview converted focal position to natural-image
coordinates (didn't account for the zoom-independent anchor point).

Fixed both the crop editor's own math and includes/photo.php's
photo_crop_style() (used for every final render — cards, previews) to
drop the origin back to the CSS default and use the correct geometry.
clampFocal() also simplifies to a plain [0,100] clamp — under real
object-position semantics that's always a valid, fully-covered crop at
any zoom >= 1, no image-dimension-dependent math needed.

Verified in a standalone test harness: dragging now reaches all the way
to an image's edges, zoom stays synced between the editor's live frame
and its reference-rectangle preview, and the applied result matches the
editor's preview exactly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

includes/photo.php

@@ -19,8 +19,12 @@ function photo_crop_style(array $row): string {
     $y    = max(0, min(100, $y));
     $zoom = max(1, min(3, $zoom));
 
+    // transform-origin is deliberately left at its CSS default (50% 50% —
+    // the box's own center), not tied to $x/$y: object-position places the
+    // unzoomed crop, and the scale transform then magnifies around whatever
+    // is currently centered, matching the crop editor exactly.
     return sprintf(
-        'object-position:%.2f%% %.2f%%;transform:scale(%.3f);transform-origin:%.2f%% %.2f%%;',
-        $x, $y, $zoom, $x, $y
+        'object-position:%.2f%% %.2f%%;transform:scale(%.3f);',
+        $x, $y, $zoom
     );
 }