Fix: ensure temp file created during script instrumentation is always cleaned up

[YUVRAJ-SINGH-3178]

Summary: Fixes a temp-file leak when script instrumentation creates a temporary file but writing to it fails. The code now tracks the created temp path and always passes that path into cleanup so orphaned .tmp_run_*.sh files are removed on error/finally paths.

• Problem: instrumentation uses tempfile.mkstemp() and assigns run_path = temp_path only on successful write; if the write fails the code falls back to full_path and the created temp file can be left on disk.
• Change: track temp_path_created when a temp file is created and pass it to _cleanup_execution() (used on error paths and in finally) so the temp file is unlinked regardless of run_path reassignment.
• Files changed: app.py (script run / instrumentation / cleanup)
• Behavioral impact: no functional behavior change when instrumentation succeeds; prevents orphaned temp files on write failure.

How to test locally

1. Start the backend.
2. Trigger a scripted run that exercises instrumentation.
3. Simulate a write failure (e.g., make the script directory unwritable or fill disk).
4. Confirm no .tmp_run_*.sh files remain after the run or error path.

closes Issue #196

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