Implement clean NixOS rebuild tmux popup

- Replace complex ASCII logo with simple text header
- Remove extra blank lines for compact display
- Left-align text for clean appearance
- Add spacing after target line for readability
- Simplify heredoc format for better maintainability

Cargo.lock

@@ -270,7 +270,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.38"
+version = "0.1.39"
 dependencies = [
  "anyhow",
  "chrono",
@@ -291,7 +291,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.38"
+version = "0.1.39"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -314,7 +314,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.38"
+version = "0.1.39"
 dependencies = [
  "chrono",
  "serde",