Refresh OpenCode Databricks tokens on demand

[rohita5l]

Summary

• replace periodic OpenCode config rewrites with an auto-discovered provider fetch plugin that caches and refreshes Databricks credentials
• refresh near expiry and retry once with a forced refresh after a 401
• require OpenCode 1.0.220+, install/update only stable v1 releases, and avoid the broken npm beta tag
• add a live end-to-end test that starts with a rejected token and proves OpenCode refreshes and retries successfully

Testing

• focused suite: 342 passed
• live staging 401 refresh e2e: passed
• Ruff and git diff checks: passed