feat: add issue kanban/attachments/deadlines, dashboard widget DnD, and checklisten system

frontend/src/pages/IssueNeu.tsx

@@ -121,6 +121,16 @@ export default function IssueNeu() {
                 </Select>
               </FormControl>
             </Grid>
+            <Grid item xs={12} sm={6}>
+              <TextField
+                label="Fällig am"
+                type="date"
+                fullWidth
+                value={form.faellig_am || ''}
+                onChange={(e) => setForm({ ...form, faellig_am: e.target.value || null })}
+                InputLabelProps={{ shrink: true }}
+              />
+            </Grid>
           </Grid>
 
           <Box sx={{ display: 'flex', justifyContent: 'flex-end', gap: 1, mt: 1 }}>