docs: fix missing media inputs in TechJournalist notebook

[danyalahmed1995]

Summary

Fixes #536.

This updates the Phi-4 multimodal TechJournalist notebook so the image and audio inputs no longer rely on missing local files.

Changes

• Adds a lightweight setup cell that creates a local media/ directory.
• Downloads sample image/audio media only when missing.
• Replaces the previous hard-coded missing paths with explicit image_path and audio_path variables.
• Keeps the existing notebook flow unchanged.
• Does not add binary files to the repo.

Validation

• Parsed the updated notebook JSON successfully.
• Verified the old ./copilot.png and ./satya1.mp3 references are no longer used by the loading cells.
• Verified the new image_path, audio_path, media_dir, and urllib.request setup references exist.
• Ran a temp-directory smoke test for download, Image.open(...), and soundfile.read(...).

Note: local validation initially required installing soundfile, then the smoke test passed after explicitly closing the image handle before temp cleanup.