Add drag-to-pan + zoom photo repositioning for card/avatar crops

Every photo upload (session setup, novena group, Rosary Builder title
photo) gets shown two ways: full-size on the presentation cover slide
(unaffected, stays untouched), and cropped to a fixed box everywhere else
— home page cards, profile cards, the novena day-picker's circular hero
photo, and each admin form's own preview thumbnail. All of those crops
used to just take the image's dead center, with no way to control what
part of the photo that was — cropping out people's heads on portrait
photos.

- New sessions/novena_groups columns: photo_focal_x, photo_focal_y (0-100%),
  photo_zoom (1-3x), defaulting to 50/50/1 — today's exact centered/
  unzoomed behavior, so this is fully backward compatible until someone
  actively repositions a photo.

- New assets/js/photo-crop.js: a reusable drag-to-pan + zoom modal editor.
  The crop frame renders with the *exact* CSS recipe used at final render
  time (object-position + transform:scale/transform-origin), so the editor
  is a truthful live preview, not an approximation. A reference thumbnail
  shows the full photo dimmed outside a rectangle marking the current crop.
  All math reads actual rendered box dimensions rather than assuming fixed
  pixel sizes, so it holds up responsively at any viewport width — caught
  and fixed a real mismatch bug here by testing the widget standalone in a
  browser before wiring it into any PHP form.

- New includes/photo.php: photo_crop_style() builds the inline style="..."
  from a session/group row, used everywhere a crop is displayed.

- Wired into all three upload locations (admin/setup.php,
  admin/novena_group.php, admin/builder.php) with a "Reposition" button,
  and persisted through api/save_session.php, admin/novena_group.php's
  save handler, and api/builder_session.php.

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

includes/photo.php

@@ -0,0 +1,26 @@
+<?php
+/**
+ * includes/photo.php — shared helper for the photo reposition/zoom feature.
+ */
+
+/**
+ * Build the inline style="" value that applies a session/novena_group row's
+ * stored crop (photo_focal_x/photo_focal_y/photo_zoom) to an <img> using
+ * object-fit: cover. Falls back to 50/50/1 (dead center, no zoom — today's
+ * default behavior) when the row predates this feature or the values are
+ * otherwise missing, so old photos render exactly as they always have.
+ */
+function photo_crop_style(array $row): string {
+    $x    = isset($row['photo_focal_x']) && $row['photo_focal_x'] !== null ? (float)$row['photo_focal_x'] : 50.0;
+    $y    = isset($row['photo_focal_y']) && $row['photo_focal_y'] !== null ? (float)$row['photo_focal_y'] : 50.0;
+    $zoom = isset($row['photo_zoom'])    && $row['photo_zoom']    !== null ? (float)$row['photo_zoom']    : 1.0;
+
+    $x    = max(0, min(100, $x));
+    $y    = max(0, min(100, $y));
+    $zoom = max(1, min(3, $zoom));
+
+    return sprintf(
+        'object-position:%.2f%% %.2f%%;transform:scale(%.3f);transform-origin:%.2f%% %.2f%%;',
+        $x, $y, $zoom, $x, $y
+    );
+}