Replace CPU frequency with C-state monitoring

- Changed CpuData.frequency_mhz to CpuData.cstate (String)
- Implemented collect_cstate() to read CPU idle depth from sysfs
- Finds deepest C-state with most accumulated time (C0-C10)
- Updated dashboard to display C-state instead of frequency
- More accurate indicator of CPU activity vs power management

Bump version to v0.1.208

Co-Authored-By: Claude <noreply@anthropic.com>

shared/src/agent_data.rs

@@ -46,7 +46,7 @@ pub struct CpuData {
     pub load_1min: f32,
     pub load_5min: f32,
     pub load_15min: f32,
-    pub frequency_mhz: f32,
+    pub cstate: String, // Deepest C-state in use (C1, C6, C10, etc.) - indicates CPU idle depth
     pub temperature_celsius: Option<f32>,
     pub load_status: Status,
     pub temperature_status: Status,
@@ -204,7 +204,7 @@ impl AgentData {
                     load_1min: 0.0,
                     load_5min: 0.0,
                     load_15min: 0.0,
-                    frequency_mhz: 0.0,
+                    cstate: String::from("C0"),
                     temperature_celsius: None,
                     load_status: Status::Unknown,
                     temperature_status: Status::Unknown,