Add Bung 2nd Coding Competition Pacman entry

[PreceptusHarmony]

This adds and improves entries from Bung Enterprises' 2nd Game Boy Coding Competition for #184.

The archived Bung results page lists several remaining missing or ambiguous entries. This PR now covers:

• Pacman (pacman.gbc): adds a new Dark Fader Pacman entry from GameBrew.
• Pong: keeps the existing old Pong.gb entry, adds the Bung/CGB version from GameBrew, adds screenshots, and tags it with event:bung-2nd-coding-compo.
• Guess: confirms the existing guess-the-number-1 ROM matches GameBrew's Guess download, then adds the Guess alias, description, and source page.
• Arkanoid: confirms the existing arkanoid-clone entry corresponds to the Bung competition entry, then adds the event tag, source page, date, description, and an extra screenshot.

Sources:

• https://www.gamebrew.org/wiki/Pacman_GB
• https://www.gamebrew.org/wiki/Pong_GB
• https://www.gamebrew.org/wiki/Guess_GB
• https://www.gamebrew.org/wiki/Arkanoid_Clone_GB

Local checks:

• PYTHONUTF8=1 python validate_schema.py
• PYTHONUTF8=1 python check_files.py
• PYTHONUTF8=1 python dupe_finder.py

Note: dupe_finder.py printed existing duplicate warnings in unrelated entries and exited successfully.

Closes #184.