feat: add datapoint delete, show emoji icons in preview

- DELETE /api/datapoints/:id endpoint + frontend button
- Preview shows emoji symbols instead of [icon] text

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

display/middleware/src/api/routes/datapoints.ts

@@ -3,6 +3,7 @@ import {
   getAllDatapoints,
   getDatapointById,
   updateDatapoint,
+  deleteDatapoint,
 } from '../../modules/datapoints/datapoint-manager';
 
 const router = Router();
@@ -38,4 +39,15 @@ router.put('/:id', (req, res): void => {
   }
 });
 
+// DELETE /api/datapoints/:id
+router.delete('/:id', (req, res): void => {
+  try {
+    const deleted = deleteDatapoint(parseInt(req.params.id));
+    if (!deleted) { res.status(404).json({ error: 'Datapoint not found' }); return; }
+    res.status(204).send();
+  } catch (err) {
+    res.status(500).json({ error: (err as Error).message });
+  }
+});
+
 export default router;

display/middleware/src/modules/datapoints/datapoint-manager.ts

@@ -118,6 +118,12 @@ export function createDatapointFromPg(
   return db.prepare('SELECT * FROM datapoints WHERE id = ?').get(id) as Datapoint;
 }
 
+export function deleteDatapoint(id: number): boolean {
+  const db = getDb();
+  const result = db.prepare('DELETE FROM datapoints WHERE id = ?').run(id);
+  return (result.changes as number) > 0;
+}
+
 export function getDatapointByTopicId(topicId: number): Datapoint | undefined {
   const db = getDb();
   return db