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/text-field.php

@@ -0,0 +1,56 @@
+<?php
+/**
+ * Text field partial — single-line text / number / url / email input.
+ *
+ * Variables consumed:
+ *   string       $name         — input name attribute (also used for id)
+ *   string       $label        — visible label text
+ *   string       $value        — current value (already htmlspecialchars'd by caller, or raw)
+ *   string       $type         — input type; default 'text'
+ *   bool         $required     — whether the field is required; default false
+ *   string       $placeholder  — placeholder text; default ''
+ *   string|null  $hint         — optional hint shown in <small> below the input
+ *   string|null  $id           — override the id attribute (defaults to $name)
+ *   array        $attrs        — extra HTML attributes as key=>value pairs (e.g. min/max for number)
+ *
+ * The partial does NOT call htmlspecialchars on $value — the caller is responsible.
+ */
+
+$type        = $type        ?? 'text';
+$required    = $required    ?? false;
+$placeholder = $placeholder ?? '';
+$hint        = $hint        ?? null;
+$id          = $id          ?? $name;
+$attrs       = $attrs       ?? [];
+
+$attrStr = '';
+foreach ($attrs as $k => $v) {
+    $attrStr .= ' ' . htmlspecialchars($k) . '="' . htmlspecialchars((string)$v) . '"';
+}
+?>
+<div>
+    <label for="<?= htmlspecialchars($id) ?>"><?= htmlspecialchars($label) ?></label>
+    <?php if ($hint): ?>
+    <div>
+        <input type="<?= htmlspecialchars($type) ?>"
+               id="<?= htmlspecialchars($id) ?>"
+               name="<?= htmlspecialchars($name) ?>"
+               value="<?= $value ?>"
+               <?= $required ? 'required' : '' ?>
+               <?= $placeholder ? 'placeholder="' . htmlspecialchars($placeholder) . '"' : '' ?>
+               <?= $attrStr ?>>
+        <small><?= htmlspecialchars($hint) ?></small>
+    </div>
+    <?php else: ?>
+    <input type="<?= htmlspecialchars($type) ?>"
+           id="<?= htmlspecialchars($id) ?>"
+           name="<?= htmlspecialchars($name) ?>"
+           value="<?= $value ?>"
+           <?= $required ? 'required' : '' ?>
+           <?= $placeholder ? 'placeholder="' . htmlspecialchars($placeholder) . '"' : '' ?>
+           <?= $attrStr ?>>
+    <?php endif; ?>
+</div>
+<?php
+// Reset consumed variables so includes in a loop don't bleed state.
+unset($type, $required, $placeholder, $hint, $id, $attrs, $attrStr, $k, $v);