Complete unified pool visualization with filesystem children

- Implement filesystem children display under physical drive pools
- Agent generates individual filesystem metrics for each mount point
- Dashboard parses filesystem metrics and displays as tree children
- Add filesystem usage, total, and available space metrics
- Support target format: drive info + filesystem children hierarchy
- Fix compilation warnings by properly using available_bytes calculation

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.100"
+version = "0.1.102"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.100"
+version = "0.1.102"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -324,7 +324,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.100"
+version = "0.1.103"
 dependencies = [
  "chrono",
  "serde",