Support multiple concurrent torrent copy operations

Update monitoring to handle multiple simultaneous torrent copy operations
using the new directory-based marker structure.

Changes:
- Rename get_active_torrent_copy() to get_active_torrent_copies()
- Read all marker files from /tmp/torrent-copy/ directory
- Return Vec<String> instead of Option<String> for multiple copies
- Display each active copy as separate sub-service
- Unsanitize filenames by replacing _ with /

This enables monitoring when multiple torrents finish simultaneously
and are being copied in parallel to permanent storage.

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.257"
+version = "0.1.258"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.257"
+version = "0.1.258"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -325,7 +325,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.257"
+version = "0.1.258"
 dependencies = [
  "chrono",
  "serde",