feat: implement Phase 3 - Batch Operations

Features added:
- Multi-select functionality for processes with checkboxes
- Floating BatchActions toolbar appears when processes are selected
- Batch operations: Start Selected, Stop Selected, Restart Selected
- Select All / Deselect All button in processes page
- Visual feedback with ring indicator on selected cards
- Click card to toggle selection, buttons prevent card selection

Implementation details:
- Created batch API routes: /api/supervisor/processes/{start-all,stop-all,restart-all}
- Added React Query hooks: useStartAllProcesses, useStopAllProcesses, useRestartAllProcesses
- Created BatchActions component with floating toolbar
- Enhanced ProcessCard with optional selection mode (isSelected, onSelectionChange props)
- Updated processes page with selection state management
- Checkbox prevents event bubbling to avoid conflicts with action buttons

UX improvements:
- Selected cards show primary ring with offset
- BatchActions toolbar slides up from bottom
- Selection count displayed in toolbar
- Clear selection with X button or after batch action completes

Phase 3 complete (4-6 hours estimated)

lib/hooks/useSupervisor.ts

@@ -370,3 +370,89 @@ export function useRestartProcessGroup() {
     },
   });
 }
+
+// Batch Operations (All Processes)
+
+async function startAllProcesses(wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch('/api/supervisor/processes/start-all', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ wait }),
+  });
+  if (!response.ok) {
+    const error = await response.json();
+    throw new Error(error.error || 'Failed to start all processes');
+  }
+  return response.json();
+}
+
+async function stopAllProcesses(wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch('/api/supervisor/processes/stop-all', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ wait }),
+  });
+  if (!response.ok) {
+    const error = await response.json();
+    throw new Error(error.error || 'Failed to stop all processes');
+  }
+  return response.json();
+}
+
+async function restartAllProcesses(wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch('/api/supervisor/processes/restart-all', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ wait }),
+  });
+  if (!response.ok) {
+    const error = await response.json();
+    throw new Error(error.error || 'Failed to restart all processes');
+  }
+  return response.json();
+}
+
+export function useStartAllProcesses() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (wait: boolean = true) => startAllProcesses(wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to start all processes: ${error.message}`);
+    },
+  });
+}
+
+export function useStopAllProcesses() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (wait: boolean = true) => stopAllProcesses(wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to stop all processes: ${error.message}`);
+    },
+  });
+}
+
+export function useRestartAllProcesses() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (wait: boolean = true) => restartAllProcesses(wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to restart all processes: ${error.message}`);
+    },
+  });
+}