fix(scrapers): resolve an alias-keyed user to the real account and fold alias-twin researchers

[quntao-z]

Closes #4988

What changes

• Readers: joinUserIdentityToExistingResearcher and resolveInferredPiKeyIdentity no longer let a local-part netid stop at its own twin account.
  When the key's netid is an email local part and resolveNetidForRosterEmailAlias resolves it to a different live account, that account wins.
  Only local-part netids that already reach an account pay the extra lookup, which is 8 accounts on Development.
• researcher-dedupe folds an alias-twin researcher into the real one through its existing merge path (edges repointed or archived as redundant, attributes unioned, roster rows re-gated).
  The alias map only proposes, because it reads every email observation including a lane that has attached a namesake's profile, so the two display names must also agree, using the fix(scripts): fold researcher duplicates split by an unprobed link or a compound surname #4920 surname rule plus a given name found among the other record's given names.
  A twin account that has signed in is refused.
• The archived twin researcher drops its accountId, because the index allows one researcher per account and accounts:merge-local-part-netid-twins (fix(accounts): refuse minting a non-netid account and merge local-part twins #4782) repoints that field when it merges the twin account next; that tool refused these exact pairs as both-accounts-link-a-researcher.

Measured on Development (dry run)

• researcher-dedupe plans 3 alias-twin folds, the 3 the gate reports.
  Refused: 4 local-part accounts whose alias does not resolve, 1 whose resolved account is not live.
• Integration test: the reader reaches the real researcher, and after the fold the alias key still reaches a live record, also with the twin account archived; reverting the reader change fails it.

Data operation

Stored-data fix: run researcher-dedupe (researchers:dedupe-accountless-shells --apply), then accounts:merge-local-part-netid-twins --apply, on Development, and verify integrity-gate duplicatePeople and the observation keys still resolving.

[github-actions]

Approved automatically: the author holds the Admin repository role (#4512).