Retarget lexicon publisher to the dedicated lexicon account on the governance PDS

[aaronstevenwhite]

Summary

A previous run mistakenly published the pub.chive.* lexicons into the chive.pub Bluesky-bot account on pds.chive.pub (that account is only for Bluesky posts). They belong in a dedicated lexicon account on the governance PDS (governance.chive.pub).

This updates the code that assumed the lexicons live in pds.chive.pub:

• scripts/publish-lexicons.ts: default LEXICON_PDS_URL → https://governance.chive.pub, LEXICON_PUBLISH_IDENTIFIER → lexicons.governance.chive.pub (both still env-overridable); doc/comments updated.
• governance-pds-writer.ts: fixed a stale pds.chive.pub JSDoc example.

No runtime code resolves pub.chive.* from pds.chive.pub (verified), so this is the only operational assumption. The did:web:chive.pub lexicon-serving handlers (loader.ts + com.atproto.repo.*) are a separate mechanism and untouched.

Operational steps (account creation on the governance PDS, publishing the 205 records, and repointing the _lexicon.chive.pub DNS TXT to the new DID) are done out-of-band; this PR is just the code retarget.

Type of Change

• Bug fix (non-breaking)

How Has This Been Tested?

• tsc --noEmit + prettier clean on changed files.

Checklist

General

• Self-review
• Lint passes
• Docs/TSDoc updated

ATProto Compliance

• No writes to user PDSes (publishes only to Chive's own lexicon account)
• Indexes rebuildable from firehose

Breaking Changes

• N/A