refactor(twitter-digest): use BankOfAI xurl npm beta

[boboliu-1010]

Summary

• reduce twitter-digest to the xurl-only execution layer
• install pinned @bankofai/xurl@1.3.2-beta.1 through npm
• bundle the native xurl binary so normal digest runs need no Node.js or Python

Verification

• isolated npm install reports xurl 1.3.2-beta.1
• skill validator passes
• encrypted X Chat keys, conversations, and read with --no-mark-read pass locally
• diff is limited to twitter-digest/