fix: resolve @te-btc packages from npm registry instead of local symlinks

package-lock.json had local symlink entries ("resolved": "../cashu-l402")
for @te-btc/cashu-l402 and @te-btc/agent-wallet, which broke Vercel builds
since those sibling directories don't exist in the CI environment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ArxMint Worker