feat(stacks): add optional volume prune to delete confirmation (#788)

The Delete Stack dialog now includes an opt-in checkbox to also remove
associated Docker volumes when the stack is deleted. The checkbox is
unchecked by default and resets to unchecked on every open.

Backend: DELETE /stacks/:name accepts ?pruneVolumes=true and calls
pruneManagedOnly for volumes labeled with the stack project name after
bringing the stack down. Prune failure is non-fatal and logged; the
delete proceeds regardless.

backend/src/routes/stacks.ts

@@ -526,6 +526,7 @@ stacksRouter.delete('/:stackName', async (req: Request, res: Response) => {
   if (!isValidStackName(stackName)) {
     return res.status(400).json({ error: 'Invalid stack name' });
   }
+  const pruneVolumes = req.query.pruneVolumes === 'true';
   try {
     try {
       await ComposeService.getInstance(req.nodeId).downStack(stackName);
@@ -533,6 +534,15 @@ stacksRouter.delete('/:stackName', async (req: Request, res: Response) => {
       console.warn(`[Teardown] Docker down failed or nothing to clean up for ${stackName}`);
     }
 
+    if (pruneVolumes) {
+      try {
+        const result = await DockerController.getInstance().pruneManagedOnly('volumes', [stackName]);
+        console.log(`[Stacks] Pruned volumes for ${stackName}: ${result.reclaimedBytes} bytes reclaimed`);
+      } catch (pruneErr) {
+        console.warn(`[Stacks] Volume prune failed for ${stackName}, continuing delete:`, pruneErr);
+      }
+    }
+
     let fsErr: unknown = null;
     try {
       await FileSystemService.getInstance(req.nodeId).deleteStack(stackName);