Update version to 0.1.21 and fix dashboard data caching

- Separate dashboard updates from email notifications for immediate status aggregation
- Add metric caching to MetricCollectionManager for instant dashboard updates
- Dashboard now receives cached data every 1 second instead of waiting for collection intervals
- Fix transmission to use cached metrics rather than triggering fresh collection
- Email notifications maintain separate 60-second batching interval
- Update configurable email notification aggregation interval

Cargo.lock

@@ -270,7 +270,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.19"
+version = "0.1.20"
 dependencies = [
  "anyhow",
  "chrono",
@@ -291,7 +291,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.19"
+version = "0.1.20"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -314,7 +314,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.19"
+version = "0.1.20"
 dependencies = [
  "chrono",
  "serde",