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)

components/process/BatchActions.tsx

@@ -0,0 +1,110 @@
+'use client';
+
+import { ProcessInfo } from '@/lib/supervisor/types';
+import { useStartProcess, useStopProcess, useRestartProcess } from '@/lib/hooks/useSupervisor';
+import { Button } from '@/components/ui/button';
+import { Card } from '@/components/ui/card';
+import { Play, Square, RotateCw, X } from 'lucide-react';
+import { cn } from '@/lib/utils/cn';
+
+interface BatchActionsProps {
+  selectedProcesses: Set<string>;
+  processes: ProcessInfo[];
+  onClearSelection: () => void;
+}
+
+export function BatchActions({ selectedProcesses, processes, onClearSelection }: BatchActionsProps) {
+  const startMutation = useStartProcess();
+  const stopMutation = useStopProcess();
+  const restartMutation = useRestartProcess();
+
+  const isLoading = startMutation.isPending || stopMutation.isPending || restartMutation.isPending;
+
+  const selectedCount = selectedProcesses.size;
+
+  if (selectedCount === 0) return null;
+
+  const handleStartSelected = async () => {
+    for (const processId of selectedProcesses) {
+      startMutation.mutate({ name: processId });
+    }
+    onClearSelection();
+  };
+
+  const handleStopSelected = async () => {
+    for (const processId of selectedProcesses) {
+      stopMutation.mutate({ name: processId });
+    }
+    onClearSelection();
+  };
+
+  const handleRestartSelected = async () => {
+    for (const processId of selectedProcesses) {
+      restartMutation.mutate(processId);
+    }
+    onClearSelection();
+  };
+
+  return (
+    <div className="fixed bottom-6 left-1/2 -translate-x-1/2 z-50 animate-slide-up">
+      <Card className="shadow-2xl border-2">
+        <div className="flex items-center gap-4 px-6 py-4">
+          <div className="flex items-center gap-2">
+            <div className="h-8 w-8 rounded-full bg-primary/10 flex items-center justify-center">
+              <span className="text-sm font-bold text-primary">{selectedCount}</span>
+            </div>
+            <span className="text-sm font-medium">
+              {selectedCount} {selectedCount === 1 ? 'process' : 'processes'} selected
+            </span>
+          </div>
+
+          <div className="h-6 w-px bg-border" />
+
+          <div className="flex gap-2">
+            <Button
+              variant="success"
+              size="sm"
+              onClick={handleStartSelected}
+              disabled={isLoading}
+              className="gap-2"
+            >
+              <Play className="h-4 w-4" />
+              Start Selected
+            </Button>
+            <Button
+              variant="destructive"
+              size="sm"
+              onClick={handleStopSelected}
+              disabled={isLoading}
+              className="gap-2"
+            >
+              <Square className="h-4 w-4" />
+              Stop Selected
+            </Button>
+            <Button
+              variant="outline"
+              size="sm"
+              onClick={handleRestartSelected}
+              disabled={isLoading}
+              className="gap-2"
+            >
+              <RotateCw className={cn('h-4 w-4', isLoading && 'animate-spin')} />
+              Restart Selected
+            </Button>
+          </div>
+
+          <div className="h-6 w-px bg-border" />
+
+          <Button
+            variant="ghost"
+            size="icon"
+            onClick={onClearSelection}
+            className="h-8 w-8"
+          >
+            <X className="h-4 w-4" />
+          </Button>
+        </div>
+      </Card>
+    </div>
+  );
+}