Add admin form field partials and apply to add/edit forms

Four reusable PHP partials extracted to templates/partials/form/:

- text-field.php  — single-line input (text/number/url); wraps input+hint in div,
                    skips the inner wrapper when no hint is present. Supports $type,
                    $placeholder, $required, $attrs, $hint, $id overrides.
- select-field.php — <select> with leading empty option; matches $selected against
                    option id OR option name string (handles view-sourced data where
                    orientation/ap/finality come back as name strings, not FK ids).
- checkbox-list.php — checkbox group (languages, formats); renders .admin-checkbox-list
                    with typed-string comparison so int ids from DB match string values.
- file-field.php  — file input with accept/multiple/hint; appends [] to name when
                    $multiple is true.

Both add.php and edit.php rewritten to use the partials:
- ~15 repeated text-field divs collapsed to single-line include calls
- ~6 repeated select divs collapsed to single-line include calls
- 4 checkbox-list blocks collapsed to 2 calls each
- 3 file input blocks collapsed to single-line include calls
- Textarea fields (synopsis, context_note) kept inline — no partial for <textarea>
- Banner preview block in edit.php kept inline — conditional UI not generalised

Line count: add.php 251→93 (-158), edit.php 289→171 (-118)

templates/partials/form/select-field.php

@@ -0,0 +1,49 @@
+<?php
+/**
+ * Select field partial.
+ *
+ * Variables consumed:
+ *   string  $name         — select name attribute (also used for id)
+ *   string  $label        — visible label text
+ *   array   $options      — each element must have 'id' and 'name' keys;
+ *                           may optionally have 'code' for display suffix
+ *   mixed   $selected     — currently selected value (compared to option 'id');
+ *                           pass null or '' for no selection
+ *   bool    $required     — whether the field is required; default false
+ *   string  $placeholder  — text for the leading empty <option>; default ''
+ *                           set to null to suppress the empty option entirely
+ *   string|null $id       — override the id attribute (defaults to $name)
+ *   string|null $hint     — optional hint shown in <small> below the select
+ */
+
+$required    = $required    ?? false;
+$placeholder = array_key_exists('placeholder', get_defined_vars()) ? $placeholder : '';
+$id          = $id          ?? $name;
+$hint        = $hint        ?? null;
+?>
+<div>
+    <label for="<?= htmlspecialchars($id) ?>"><?= htmlspecialchars($label) ?></label>
+    <select id="<?= htmlspecialchars($id) ?>"
+            name="<?= htmlspecialchars($name) ?>"
+            <?= $required ? 'required' : '' ?>>
+        <?php if ($placeholder !== null): ?>
+        <option value=""><?= htmlspecialchars($placeholder) ?></option>
+        <?php endif; ?>
+        <?php foreach ($options as $opt): ?>
+        <?php
+            // Match by id (numeric FK) or by name string (when the view returns the name).
+            $isSelected = ((string)$selected === (string)$opt['id'])
+                       || ($selected !== null && $selected !== '' && isset($opt['name']) && (string)$selected === (string)$opt['name']);
+        ?>
+        <option value="<?= htmlspecialchars((string)$opt['id']) ?>"
+            <?= $isSelected ? 'selected' : '' ?>>
+            <?= htmlspecialchars($opt['name']) ?><?php if (!empty($opt['code'])): ?> (<?= htmlspecialchars($opt['code']) ?>)<?php endif; ?>
+        </option>
+        <?php endforeach; ?>
+    </select>
+    <?php if ($hint): ?>
+    <small><?= htmlspecialchars($hint) ?></small>
+    <?php endif; ?>
+</div>
+<?php
+unset($required, $placeholder, $id, $hint);