feat: implement Phase 2 - Process Groups Management

Features added:
- Group-based process organization with collapsible cards
- Batch operations for groups (Start All, Stop All, Restart All)
- Group statistics display (running, stopped, fatal counts)
- Dedicated /groups page for group-centric management
- View toggle in /processes page (Flat view | Grouped view)

Implementation details:
- Created group API routes: /api/supervisor/groups/[name]/{start,stop,restart}
- Added React Query hooks: useStartProcessGroup, useStopProcessGroup, useRestartProcessGroup
- Created components: GroupCard, GroupView, GroupSelector
- Updated Navbar with Groups navigation link
- Integrated grouped view in processes page with toggle

Phase 2 complete (6-8 hours estimated)

lib/hooks/useSupervisor.ts

@@ -284,3 +284,89 @@ export function useClearAllLogs() {
     },
   });
 }
+
+// Process Group Management
+
+async function startProcessGroup(name: string, wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch(`/api/supervisor/groups/${encodeURIComponent(name)}/start`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ wait }),
+  });
+  if (!response.ok) {
+    const error = await response.json();
+    throw new Error(error.error || 'Failed to start process group');
+  }
+  return response.json();
+}
+
+async function stopProcessGroup(name: string, wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch(`/api/supervisor/groups/${encodeURIComponent(name)}/stop`, {
+    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 process group');
+  }
+  return response.json();
+}
+
+async function restartProcessGroup(name: string, wait: boolean = true): Promise<{ success: boolean; message: string; results: any[] }> {
+  const response = await fetch(`/api/supervisor/groups/${encodeURIComponent(name)}/restart`, {
+    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 process group');
+  }
+  return response.json();
+}
+
+export function useStartProcessGroup() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: ({ name, wait }: { name: string; wait?: boolean }) => startProcessGroup(name, wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to start process group: ${error.message}`);
+    },
+  });
+}
+
+export function useStopProcessGroup() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: ({ name, wait }: { name: string; wait?: boolean }) => stopProcessGroup(name, wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to stop process group: ${error.message}`);
+    },
+  });
+}
+
+export function useRestartProcessGroup() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: ({ name, wait }: { name: string; wait?: boolean }) => restartProcessGroup(name, wait),
+    onSuccess: (data) => {
+      toast.success(data.message);
+      queryClient.invalidateQueries({ queryKey: supervisorKeys.processes() });
+    },
+    onError: (error: Error) => {
+      toast.error(`Failed to restart process group: ${error.message}`);
+    },
+  });
+}