Fix unified pool visualization filesystem children display issues

- Fix extract_pool_name() to handle filesystem metrics (_fs_) correctly
- Prevent individual filesystem pools (nvme0n1_fs_boot, nvme0n1_fs_root) from being created
- Fix incorrect mount point names (was showing /root/mount instead of /)
- Only create filesystem entries when receiving mount_point metrics
- Add available_gb field to FileSystem struct for proper available space handling
- Ensure filesystem children show correct usage data instead of —% —GB/—GB

Cargo.lock

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