fix: replace personal and generic placeholders with realistic examples

[zaccesss]

Replaces all personal or weak placeholder text across the three form pages with realistic, generic examples.

Field	Before	After
Full Name (register)	e.g. Isaac Adjei	e.g. Alex Johnson
Email (register + login)	e.g. yourname@aston.ac.uk	e.g. alex.johnson@aston.ac.uk
Key programming (register)	e.g. Python, C++, Java	e.g. Python (singular - matches update.php)
Profile summary (register)	Write a short summary about yourself	Full realistic example sentence
Links (register + update)	e.g. https://github.com/yourusername	e.g. https://github.com/alexjohnson, https://linkedin.com/in/alexjohnson