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>

Cargo.lock

@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.206"
+version = "0.1.207"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -324,7 +324,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.206"
+version = "0.1.207"
 dependencies = [
  "chrono",
  "serde",