Switch translation PR identity to quantecon-services machine user

[mmcky]

Summary

Translation PRs in target repos (e.g., lecture-python-programming.zh-cn) currently appear under mmcky because the sync workflow uses a PAT owned by that personal account. These should come from the quantecon-services machine user instead.

Current State

Sync mode requires a PAT for cross-repo access. The PAT is stored as a repo secret (e.g., QUANTECON_SERVICES_PAT or TRANSLATION_PAT) in source repos. The current PAT belongs to mmcky, so all translation PRs show that user as the author.

Steps

1. Generate a new PAT from the quantecon-services GitHub account with repo scope (or fine-grained equivalent)
2. Ensure quantecon-services has collaborator access (write) to both source and target repos
3. Update the secret in each source repo to use the new PAT:
   • QuantEcon/lecture-python-programming — update QUANTECON_SERVICES_PAT / TRANSLATION_PAT
   • Any other source repos using the action
4. Update test repo secrets — QuantEcon/test-translation-sync uses QUANTECON_SERVICES_PAT
5. Verify by triggering a test translation PR and confirming it shows as quantecon-services

Affected Repos

• QuantEcon/lecture-python-programming (source)
• QuantEcon/lecture-python-programming.zh-cn (target)
• QuantEcon/lecture-python-programming.fa (target)
• QuantEcon/test-translation-sync (test source)
• QuantEcon/test-translation-sync.zh-cn (test target)
• QuantEcon/test-translation-sync.fa (test target)