feat(rust): Redis adapter (connect + basic commands) #1892

Parent

#1850

Goal

Minimal Redis client: connect, KEYS/SCAN subset, GET/SET for smoke.

Done when

• cargo test or documented manual check

How to work

• Branch: issue/<n>-slug from epic/tauri-migration (create epic branch if missing).
• One PR → Closes #<n>.
• Target PR base: epic/tauri-migration until the SQLite slice is green.
• Do not edit Flutter app code unless this issue says so.