fix: lionbridge connector correctness/compliance fixes + test parity

[markdaugherty]

Summary

Continues the Lionbridge translation connector work from #651 (thanks @ravuthu). Fixes found by testing against the real Lionbridge Content API v2 and the real DA Translate app UI, plus compliance work against Lionbridge's dev guidelines, plus test parity with the other connectors (Trados/Smartling).

Bug fixes (found via live API testing, not caught by mocked tests):

• providerId must be sent on submit, not createJob — the API silently drops it on POST /jobs, then rejects submit with "Job is missing providerId".
• retrievefile needs Accept: application/octet-stream, not the default application/json (403s otherwise). Other endpoints are unaffected.
• auth.js now resolves the da-etc origin via the shared DA_ETC export (env-override support via ?da-etc=) instead of a hardcoded URL — needed to actually test this locally, and a real correctness fix regardless.

Compliance with Lionbridge's dev guidelines:

• Rate-limit handling: retry 429/503 with exponential backoff, honoring Retry-After.
• jobName/requestName truncated to the 250-byte limit.
• Generate and persist a per org/site/env connector GUID (in .da/translate.json, written once), prefixed onto connectorName per their connector-fingerprinting requirement.
• Call the approve endpoint after a successful download/save, closing out the request in Lionbridge's review workflow (REVIEW_TRANSLATION → TRANSLATION_APPROVED).
• No cancelTranslation export — their guidelines explicitly prohibit connectors from letting users cancel in-progress jobs; documented inline.

Test parity:

• Added auth.test.js, connectorGuid.test.js, and full index.test.js coverage for sendAllLanguages/getStatusAll/saveItems/connect (previously only statusFor had tests), matching Trados/Smartling's depth.
• Two tests directly regression-lock the providerId and Accept-header bugs above.

Verification

• Standalone scripts against real Lionbridge staging APIs: full sendAllLanguages chain (createJob → upload → addRequest → submit), getStatusAll, saveItems/retrievefile, and approve.
• Full end-to-end through the real DA Translate app UI (da.live/apps/loc) against a real test site (scdemos/lionbridge-demo — new GitHub repo + AEM Code Sync + DA content), with the backend (da-sites/da-etc#2) running locally via ?da-etc=local: created a project, sent a real page for translation, polled status to completion, and confirmed the translated copy landed at /fr/test-page.html.
• npm test (1236 tests) and lint pass.

Documentation

Lionbridge was missing from the public docs.da.live connector documentation. The following pages have draft updates pending publish (not yet live):

• Connecting to a Translation Service — added an "Available connectors" list (was previously silent on which connectors exist) and fixed the minimal-API description, which named a nonexistent getItems() instead of the saveItems() every real connector implements
• Setup translation (parent)
• Localization reference (parent)
• Sample loc configs — added a "Language-based Lionbridge config" section alongside the existing Google/Smartling/Trados samples
• Sample Lionbridge translate.json — new downloadable reference config, mirroring the Trados sample's structure with real verified authEndpoint/apiEndpoint values

Dependency

This connector can't authenticate against a real Lionbridge account until da-sites/da-etc#2 merges.

Marking as draft pending final review pass.