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)

app/api/supervisor/processes/restart-all/route.ts

@@ -0,0 +1,30 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { createSupervisorClient } from '@/lib/supervisor/client';
+
+// POST - Restart all processes (stop then start)
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json().catch(() => ({}));
+    const wait = body.wait ?? true;
+
+    const client = createSupervisorClient();
+
+    // Stop all processes first
+    await client.stopAllProcesses(wait);
+
+    // Then start them
+    const results = await client.startAllProcesses(wait);
+
+    return NextResponse.json({
+      success: true,
+      message: 'Restarted all processes',
+      results,
+    });
+  } catch (error: any) {
+    console.error('Supervisor restart all processes error:', error);
+    return NextResponse.json(
+      { error: error.message || 'Failed to restart all processes' },
+      { status: 500 }
+    );
+  }
+}