Add pi-memory extension

[tickernelz]

Adds pi-memory to the Extensions section.

pi-memory is a memory management extension for pi coding agent that provides:

• Long-term memory storage (MEMORY.md)
• AI identity management (IDENTITY.md)
• User profile context (USER.md)
• Daily logging (daily/YYYY-MM-DD.md)
• Auto context injection into system prompt

Repository: https://github.com/tickernelz/pi-memory
NPM: https://www.npmjs.com/package/@zhafron/pi-memory

Submission checklist:

• Tool is actively maintained (commits within last year)
• Has documentation / README
• Description is concise and explains value
• Link works and goes to correct resource
• Not a duplicate
• Alphabetically ordered within section