Fix path traversal and argument injection in launcher.py

[alfieprojectsdev]

This PR fixes a critical security vulnerability in field-logic/launcher.py.
The script was vulnerable to path traversal (e.g., ../) and argument injection.
The fix ensures that the resolved file path is strictly within the allowed MEDIA_DIR using os.path.abspath and os.path.commonpath.
It also validates the timestamp argument to ensure it is a valid float, preventing argument injection.
A new test file field-logic/test_launcher_security.py is added to verify the security fixes.

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PR created automatically by Jules for task 13362144094626353616 started by @alfieprojectsdev

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