feat: add template delete — backend DELETE route, frontend trash button

- DELETE /templates/:id — backend route
- deleteTemplate() API client function
- Trash icon on each template list item (shows on hover)
- Confirms inline, no dialog needed
- Resets builder if the deleted template was being edited

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/routes/templates.ts

@@ -151,6 +151,21 @@ export function createTemplatesRouter(db: Db): Hono {
     return c.json(updated);
   });
 
+  router.delete('/:id', async (c) => {
+    const id = c.req.param('id');
+
+    const existing = await db.query.templates.findFirst({
+      where: eq(templates.id, id),
+    });
+
+    if (!existing) {
+      throw new HTTPException(404, { message: 'Template not found' });
+    }
+
+    await db.delete(templates).where(eq(templates.id, id));
+    return c.json({ ok: true });
+  });
+
   router.post('/preview', async (c) => {
     const body = await c.req.json();
     const subjectTemplate = String(body.subject_template ?? '');