fix: clean up temporary compose files after conversion

[htoyoda18]

What I did

This PR fixes the temporary file handling in the bridge package during
the compose convert process.

Previously, the convert function used a fixed path in the system temporary
directory via os.TempDir(), which caused the following issues:

• Temporary compose.yaml files were not removed after execution
• Multiple runs could overwrite the same file
• Concurrent executions could lead to race conditions
• Sensitive project data could remain on disk unexpectedly

This change replaces the shared temp directory usage with
os.MkdirTemp, creating an isolated temporary directory per execution
and ensuring proper cleanup with defer os.RemoveAll.

---

Related issue

fixes #13482

---

(not mandatory) A picture of a cute animal, if possible in relation to what you did