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)

app/api/supervisor/groups/[name]/signal/route.ts

@@ -0,0 +1,37 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { createSupervisorClient } from '@/lib/supervisor/client';
+
+interface RouteParams {
+  params: Promise<{ name: string }>;
+}
+
+// POST - Send signal to all processes in a group
+export async function POST(request: NextRequest, { params }: RouteParams) {
+  try {
+    const { name } = await params;
+    const body = await request.json();
+    const { signal } = body;
+
+    if (!signal) {
+      return NextResponse.json(
+        { error: 'Signal is required' },
+        { status: 400 }
+      );
+    }
+
+    const client = createSupervisorClient();
+    const results = await client.signalProcessGroup(name, signal);
+
+    return NextResponse.json({
+      success: true,
+      message: `Signal ${signal} sent to group ${name}`,
+      results,
+    });
+  } catch (error: any) {
+    console.error('Supervisor signal process group error:', error);
+    return NextResponse.json(
+      { error: error.message || 'Failed to send signal to process group' },
+      { status: 500 }
+    );
+  }
+}

app/api/supervisor/processes/[name]/signal/route.ts

@@ -0,0 +1,36 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { createSupervisorClient } from '@/lib/supervisor/client';
+
+interface RouteParams {
+  params: Promise<{ name: string }>;
+}
+
+// POST - Send signal to a process
+export async function POST(request: NextRequest, { params }: RouteParams) {
+  try {
+    const { name } = await params;
+    const body = await request.json();
+    const { signal } = body;
+
+    if (!signal) {
+      return NextResponse.json(
+        { error: 'Signal is required' },
+        { status: 400 }
+      );
+    }
+
+    const client = createSupervisorClient();
+    const result = await client.signalProcess(name, signal);
+
+    return NextResponse.json({
+      success: result,
+      message: `Signal ${signal} sent to ${name}`,
+    });
+  } catch (error: any) {
+    console.error('Supervisor signal process error:', error);
+    return NextResponse.json(
+      { error: error.message || 'Failed to send signal to process' },
+      { status: 500 }
+    );
+  }
+}

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

@@ -0,0 +1,32 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { createSupervisorClient } from '@/lib/supervisor/client';
+
+// POST - Send signal to all processes
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json();
+    const { signal } = body;
+
+    if (!signal) {
+      return NextResponse.json(
+        { error: 'Signal is required' },
+        { status: 400 }
+      );
+    }
+
+    const client = createSupervisorClient();
+    const results = await client.signalAllProcesses(signal);
+
+    return NextResponse.json({
+      success: true,
+      message: `Signal ${signal} sent to all processes`,
+      results,
+    });
+  } catch (error: any) {
+    console.error('Supervisor signal all processes error:', error);
+    return NextResponse.json(
+      { error: error.message || 'Failed to send signal to all processes' },
+      { status: 500 }
+    );
+  }
+}