Fix data caching to prevent empty broadcasts

CRITICAL FIX: Collectors now update cached AgentData instead of
creating new empty data each cycle. This prevents the dashboard
from seeing flashing/disappearing data.

- Add cached_agent_data field to Agent struct
- Update cached data when collectors run
- Always broadcast the full cached data every 2s
- Only individual collectors respect their intervals
- Bump version to v0.1.230

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.229"
+version = "0.1.230"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.229"
+version = "0.1.230"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -325,7 +325,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.229"
+version = "0.1.230"
 dependencies = [
  "chrono",
  "serde",