feat: add Memory/GC and CPU monitoring

[rlaope]

Summary

• Add GC monitoring via jdk.GarbageCollection and jdk.GCHeapSummary JFR events
• Add CPU monitoring via jdk.CPULoad JFR event
• Add dashboard UI with GC Timeline, Heap Usage, and CPU Load charts

Changes

argus-core

• Add GC_PAUSE, GC_HEAP_SUMMARY, CPU_LOAD to EventType enum
• Create GCEvent and CPUEvent record classes

argus-agent

• Implement GCEventExtractor and CPUEventExtractor for JFR data extraction
• Update JfrStreamingEngine to capture GC/CPU events
• Add configuration options (argus.gc.enabled, argus.cpu.enabled, argus.cpu.interval)

argus-server

• Add GCAnalyzer and CPUAnalyzer for server-side metrics aggregation
• Add /gc-analysis and /cpu-metrics REST endpoints
• Extend EventBroadcaster to broadcast GC/CPU events via WebSocket

argus-frontend

• Add metric cards for GC Pauses, Heap Used, CPU (JVM)
• Add GC Timeline chart (bar chart)
• Add Heap Usage chart (line chart)
• Add CPU Load chart (line chart with JVM/System CPU)

demo metrics sample

$ ./gradlew :samples:virtual-thread-simulation:runMetricsDemo

Test plan

• Build passes (./gradlew build)
• Run server with demo application
• Verify GC metrics appear in dashboard when GC occurs
• Verify CPU metrics update every second
• Test /gc-analysis and /cpu-metrics endpoints

🤖 Generated with Claude Code