REPL: Package Hub Integration

Search and install versioned Logic Packs and models directly from the central registry.

`.hub`

Performs hub registry interactions (search, install, and list local packages).

Syntax:
- .hub search <query>
- .hub install <package_name>
- .hub list

sql

anam> .hub search fraud
financial-compliance@1.0.0 — Datalog rules and models for risk checking

sql

anam> .hub install financial-compliance
Installing financial-compliance...
✓ Package financial-compliance@1.0.0 installed to ./packs/

sql

anam> .hub list
financial-compliance@1.0.0