Art: drag pieces into a new order

Each gallery tile gets a small drag handle (top-left, ✱). Grab it and
drop it anywhere among the others - the tile moves live as you drag
over neighbours, then the new order is saved automatically on drop.

- Artwork gets a `position` column; the gallery lists by position (was
  upload date). New uploads land after everything else.
- New POST /art/reorder endpoint takes an ordered list of ids (one
  shared CSRF token, "reorder-art") and rewrites positions 1..n.
- Migration backfills position from the existing upload-date order via
  ROW_NUMBER(), then drops the bootstrap default so it matches the
  Doctrine mapping.
- New Stimulus controller (art-reorder): native HTML5 drag/drop, no
  library. dragover live-reorders the DOM by comparing cursor x to the
  hovered tile's midpoint; dragend posts the resulting id order and
  shows a small "Saving order… / Order saved" status pill.

Verified: schema validate clean: a throwaway script exercised
persist+reload of a reordered set against the real DB, and a live
browser check dispatched real DragEvents through the actual Stimulus
controller and confirmed the exact POST payload it sent. phpunit 9/9.

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

assets/controllers/art_reorder_controller.js

@@ -0,0 +1,94 @@
+import { Controller } from '@hotwired/stimulus';
+
+/*
+ * Drag-to-reorder for the art gallery.
+ *
+ *   <div data-controller="art-reorder"
+ *        data-art-reorder-url-value="/art/reorder"
+ *        data-art-reorder-token-value="...">
+ *     <div data-art-reorder-target="item" data-art-id="5">
+ *       <button draggable="true"
+ *               data-action="dragstart->art-reorder#dragStart dragend->art-reorder#dragEnd">⠿</button>
+ *       ...
+ *     </div>
+ *     ...
+ *   </div>
+ *   <div data-art-reorder-target="status"></div>
+ *
+ * The dragged tile is moved live in the DOM as the pointer crosses other
+ * tiles (dragover, bound on the grid itself via data-action); the new order
+ * is only sent to the server once, on dragend.
+ */
+export default class extends Controller {
+    static targets = ['item', 'status'];
+    static values = { url: String, token: String };
+
+    dragStart(event) {
+        const tile = event.currentTarget.closest('[data-art-reorder-target="item"]');
+        if (!tile) return;
+
+        this.dragEl = tile;
+        this.startOrder = this.currentOrder();
+        tile.classList.add('is-dragging');
+        event.dataTransfer.effectAllowed = 'move';
+        // Firefox requires data to be set for the drag to start at all.
+        event.dataTransfer.setData('text/plain', tile.dataset.artId);
+    }
+
+    dragOver(event) {
+        if (!this.dragEl) return;
+        event.preventDefault();
+
+        const over = event.target.closest('[data-art-reorder-target="item"]');
+        if (!over || over === this.dragEl) return;
+
+        const rect = over.getBoundingClientRect();
+        const before = event.clientX - rect.left < rect.width / 2;
+        over.parentNode.insertBefore(this.dragEl, before ? over : over.nextSibling);
+    }
+
+    drop(event) {
+        event.preventDefault();
+    }
+
+    dragEnd() {
+        if (!this.dragEl) return;
+        this.dragEl.classList.remove('is-dragging');
+
+        const order = this.currentOrder();
+        const changed = order.join(',') !== (this.startOrder || []).join(',');
+        this.dragEl = null;
+
+        if (changed) this.persist(order);
+    }
+
+    currentOrder() {
+        return this.itemTargets.map((el) => el.dataset.artId);
+    }
+
+    async persist(order) {
+        this.showStatus('Saving order…');
+        try {
+            const res = await fetch(this.urlValue, {
+                method: 'POST',
+                credentials: 'same-origin',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ _token: this.tokenValue, order }),
+            });
+            if (!res.ok) throw new Error(`HTTP ${res.status}`);
+            this.showStatus('Order saved');
+        } catch (e) {
+            console.error('art reorder save failed', e);
+            this.showStatus('Could not save the new order — reload and try again', true);
+        }
+    }
+
+    showStatus(text, isError = false) {
+        if (!this.hasStatusTarget) return;
+        clearTimeout(this.statusTimer);
+        this.statusTarget.textContent = text;
+        this.statusTarget.classList.toggle('is-error', isError);
+        this.statusTarget.classList.add('is-visible');
+        this.statusTimer = setTimeout(() => this.statusTarget.classList.remove('is-visible'), isError ? 4000 : 1800);
+    }
+}

assets/styles/app.css

@@ -113,6 +113,47 @@ table.dataTable {
     height: auto;
 }
 
+/* Drag-to-reorder handle, top-left of each tile */
+.art-drag-handle {
+    position: absolute;
+    top: 0.35rem;
+    left: 0.35rem;
+    z-index: 2;
+    width: 1.9rem;
+    height: 1.9rem;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    border: 1px solid var(--bs-border-color);
+    border-radius: 0.35rem;
+    background: var(--bs-body-bg);
+    color: var(--bs-secondary-color);
+    opacity: 0.8;
+    cursor: grab;
+    line-height: 1;
+}
+.art-drag-handle:hover { opacity: 1; color: var(--bs-body-color); }
+.art-drag-handle:active { cursor: grabbing; }
+.art-tile.is-dragging { opacity: 0.4; }
+.art-tile.is-drag-over .card { outline: 2px dashed var(--bs-primary); outline-offset: 2px; }
+
+.art-reorder-status {
+    position: fixed;
+    right: 1rem;
+    bottom: 1rem;
+    z-index: 1080;
+    padding: 0.4rem 0.85rem;
+    border-radius: 2rem;
+    background: var(--bs-body-color);
+    color: var(--bs-body-bg);
+    font-size: 0.85rem;
+    opacity: 0;
+    pointer-events: none;
+    transition: opacity 0.2s ease;
+}
+.art-reorder-status.is-visible { opacity: 0.92; }
+.art-reorder-status.is-error { background: var(--bs-danger); color: #fff; }
+
 /* --- Tracker: unfoldable stat blocks --------------------------------- */
 [data-bs-toggle="collapse"] .sb-caret {
     display: inline-block;