chore: sync librarian.yaml with generation_config.yaml

[zhumin8]

Sync librarian.yaml with generation_config.yaml for latest changes, including googleapis commit change, new library addition and libraries bom version.
Update librarian version, which brings in changes from googleapis/librarian#6252 and googleapis/librarian#6125.

This change is made be following steps:

• migrate . syn generation_config.yaml changes
• set librarian pseudo version

PSEUDO=$(GOPROXY=direct go list -m -f '{{.Version}}' [github.com/googleapis/librarian@main](http://github.com/googleapis/librarian@main))

For googleapis/librarian#6173

[gemini-code-assist]

Code Review

This pull request updates the googleapis source commit and sha256, bumps the libraries_bom_version to 26.83.0, and adds configuration for a new library named developerknowledge in librarian.yaml. There are no review comments, so I have no feedback to provide.

[zhumin8]

generate --all failed with "failed to identify missing modules for "developerknowledge": failed to find api config for google/developers/knowledge/v1: API google/developers/knowledge/v1 is not in allowlist" googleapis/librarian#6240 should fix it.

[zhumin8]

note: for current generation diff, tracked with googleapis/librarian#6244 needs to be fixed for future partial releases, but is not a blocker for migration this week.
After the pending new release is cut, all versions should bump to next minor.

[zhumin8]

generation diff check succeeded: https://github.com/googleapis/google-cloud-java/actions/runs/26844032681/job/79158569883?pr=13319