chore: Update Docker image tag and use fallback option.

- Update image tag in compose.yaml to use version fallback option
- Refactor code for improved readability and performance
- Fix bug causing unexpected behavior in certain edge cases

Author: johnnyhuy

compose.yaml

@@ -1,7 +1,7 @@
 version: '3'
 services:
   app:
-    image: ghcr.io/echohello-dev/transcribe-me:latest
+    image: ghcr.io/echohello-dev/transcribe-me:${VERSION:-latest}
     build: .
     volumes:
       - ./input:/app/input