Implement multi-disk backup support

- Update BackupData structure to support multiple backup disks
- Scan /var/lib/backup/status/ directory for all status files
- Calculate status icons for backup and disk usage
- Aggregate repository status from all disks
- Update dashboard to display all backup disks with per-disk status
- Display repository list with count and aggregated status

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.211"
+version = "0.1.212"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.211"
+version = "0.1.212"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -324,7 +324,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.211"
+version = "0.1.212"
 dependencies = [
  "chrono",
  "serde",