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)

components/groups/GroupView.tsx

@@ -0,0 +1,35 @@
+'use client';
+
+import { ProcessInfo } from '@/lib/supervisor/types';
+import { GroupCard } from './GroupCard';
+
+interface GroupViewProps {
+  processes: ProcessInfo[];
+}
+
+export function GroupView({ processes }: GroupViewProps) {
+  // Group processes by their group name
+  const groupedProcesses = processes.reduce((acc, process) => {
+    const groupName = process.group;
+    if (!acc[groupName]) {
+      acc[groupName] = [];
+    }
+    acc[groupName].push(process);
+    return acc;
+  }, {} as Record<string, ProcessInfo[]>);
+
+  // Sort groups alphabetically
+  const sortedGroups = Object.keys(groupedProcesses).sort();
+
+  return (
+    <div className="space-y-6">
+      {sortedGroups.map((groupName) => (
+        <GroupCard
+          key={groupName}
+          groupName={groupName}
+          processes={groupedProcesses[groupName]}
+        />
+      ))}
+    </div>
+  );
+}