Implement real-time process monitoring and fix UI hardcoded data

This commit addresses several key issues identified during development:

Major Changes:
- Replace hardcoded top CPU/RAM process display with real system data
- Add intelligent process monitoring to CpuCollector using ps command
- Fix disk metrics permission issues in systemd collector
- Optimize service collection to focus on status, memory, and disk only
- Update dashboard widgets to display live process information

Process Monitoring Implementation:
- Added collect_top_cpu_process() and collect_top_ram_process() methods
- Implemented ps-based monitoring with accurate CPU percentages
- Added filtering to prevent self-monitoring artifacts (ps commands)
- Enhanced error handling and validation for process data
- Dashboard now shows realistic values like "claude (PID 2974) 11.0%"

Service Collection Optimization:
- Removed CPU monitoring from systemd collector for efficiency
- Enhanced service directory permission error logging
- Simplified services widget to show essential metrics only
- Fixed service-to-directory mapping accuracy

UI and Dashboard Improvements:
- Reorganized dashboard layout with btop-inspired multi-panel design
- Updated system panel to include real top CPU/RAM process display
- Enhanced widget formatting and data presentation
- Removed placeholder/hardcoded data throughout the interface

Technical Details:
- Updated agent/src/collectors/cpu.rs with process monitoring
- Modified dashboard/src/ui/mod.rs for real-time process display
- Enhanced systemd collector error handling and disk metrics
- Updated CLAUDE.md documentation with implementation details

shared/src/error.rs

@@ -0,0 +1,21 @@
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum SharedError {
+    #[error("Serialization error: {message}")]
+    Serialization { message: String },
+    
+    #[error("Invalid metric value: {message}")]
+    InvalidMetric { message: String },
+    
+    #[error("Protocol error: {message}")]
+    Protocol { message: String },
+}
+
+impl From<serde_json::Error> for SharedError {
+    fn from(err: serde_json::Error) -> Self {
+        SharedError::Serialization {
+            message: err.to_string(),
+        }
+    }
+}