feat: implement Phase 7 - Signal Operations

Features added:
- Send Unix signals to processes via interactive modal
- Support for common signals (HUP, INT, TERM, KILL, USR1, USR2, QUIT)
- Custom signal input for advanced use cases
- Safety confirmations for dangerous signals (TERM, KILL, QUIT)
- Signal button added to each ProcessCard

Implementation details:
- Created signal API routes:
  - /api/supervisor/processes/[name]/signal - Send signal to process
  - /api/supervisor/groups/[name]/signal - Send signal to group
  - /api/supervisor/processes/signal-all - Send signal to all processes

- Added React Query hooks:
  - useSignalProcess() - Send signal to single process
  - useSignalProcessGroup() - Send signal to process group
  - useSignalAllProcesses() - Send signal to all processes

- Created SignalSender modal component:
  - Grid of common signal buttons with descriptions
  - Custom signal text input (auto-uppercase)
  - Two-step confirmation for dangerous signals
  - Visual warning with AlertTriangle icon
  - Destructive button variant for confirmed dangerous signals
  - Backdrop blur overlay

ProcessCard enhancements:
- Added Zap icon signal button
- Modal opens on signal button click
- Button disabled when process is stopped
- Modal integrates with useSignalProcess hook

Common signals with descriptions:
- HUP (1): Reload configuration
- INT (2): Interrupt - graceful shutdown
- QUIT (3): Quit
- TERM (15): Terminate - graceful shutdown (dangerous)
- KILL (9): Kill - immediate termination (dangerous)
- USR1 (10): User-defined signal 1
- USR2 (12): User-defined signal 2

Safety features:
- Dangerous signals require confirmation
- Warning message explains risks
- Button changes to destructive variant
- Custom signals also checked for danger
- Clear visual feedback during operation

Phase 7 complete (3-4 hours estimated)

components/process/ProcessCard.tsx

@@ -1,11 +1,13 @@
 'use client';
 
-import { Play, Square, RotateCw, Activity } from 'lucide-react';
+import { useState } from 'react';
+import { Play, Square, RotateCw, Activity, Zap } from 'lucide-react';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { Button } from '@/components/ui/button';
 import { Badge } from '@/components/ui/badge';
 import { ProcessInfo, ProcessStateCode, getProcessStateClass, formatUptime, canStartProcess, canStopProcess } from '@/lib/supervisor/types';
 import { useStartProcess, useStopProcess, useRestartProcess } from '@/lib/hooks/useSupervisor';
+import { SignalSender } from './SignalSender';
 import { cn } from '@/lib/utils/cn';
 
 interface ProcessCardProps {
@@ -15,6 +17,7 @@ interface ProcessCardProps {
 }
 
 export function ProcessCard({ process, isSelected = false, onSelectionChange }: ProcessCardProps) {
+  const [showSignalModal, setShowSignalModal] = useState(false);
   const startMutation = useStartProcess();
   const stopMutation = useStopProcess();
   const restartMutation = useRestartProcess();
@@ -131,6 +134,15 @@ export function ProcessCard({ process, isSelected = false, onSelectionChange }:
           >
             <RotateCw className={cn('h-4 w-4', isLoading && 'animate-spin-slow')} />
           </Button>
+          <Button
+            size="sm"
+            variant="outline"
+            onClick={() => setShowSignalModal(true)}
+            disabled={process.state === 0}
+            title="Send Signal"
+          >
+            <Zap className="h-4 w-4" />
+          </Button>
         </div>
 
         {/* Description */}
@@ -140,6 +152,11 @@ export function ProcessCard({ process, isSelected = false, onSelectionChange }:
           </p>
         )}
       </CardContent>
+
+      {/* Signal Modal */}
+      {showSignalModal && (
+        <SignalSender processName={fullName} onClose={() => setShowSignalModal(false)} />
+      )}
     </Card>
   );
 }