feat: add redeploy endpoint — rebuild from latest git/zip source and deploy new version

- Backend: added redeployApplication() to DeploymentsService that creates
  a new deployment record and re-runs the full build+deploy pipeline
- Backend: added POST /deployments/applications/:appId/redeploy endpoint
- Frontend: added Redeploy button on app detail page, visible after first
  deploy when no build is in progress
- For git-based apps: pulls latest code from repo on each redeploy
- For zip-based apps: rebuilds from last uploaded source code

frontend/src/app/dashboard/apps/[id]/page.tsx

@@ -94,6 +94,15 @@ export default function AppDetailPage() {
     onError: () => toast.error('Failed to restart application'),
   });
 
+  const redeployMutation = useMutation({
+    mutationFn: () => api.post(`/deployments/applications/${appId}/redeploy`),
+    onSuccess: () => {
+      invalidateAll();
+      toast.success('Redeploy triggered — building new version from latest source');
+    },
+    onError: () => toast.error('Failed to trigger redeploy'),
+  });
+
   const deleteMutation = useMutation({
     mutationFn: () => api.delete(`/applications/${appId}`),
     onSuccess: () => {
@@ -230,6 +239,18 @@ export default function AppDetailPage() {
                   {restartMutation.isPending ? '⏳...' : '🔄 Restart'}
                 </button>
               )}
+
+              {/* Redeploy: rebuild from latest git/code */}
+              {!isInProgress && (
+                <button
+                  onClick={() => redeployMutation.mutate()}
+                  disabled={redeployMutation.isPending}
+                  className="btn-primary text-sm disabled:opacity-50"
+                  title="Rebuild from latest source code and deploy new version"
+                >
+                  {redeployMutation.isPending ? '⏳ Rebuilding...' : '🔄 Redeploy'}
+                </button>
+              )}
             </>
           )}