test(workbook): qualify verified complete migration

[rudycelekli]

What & why

Snapshot every matching legacy lead during workbook migration. Read source pages of 500 and flush row batches of 50, then commit the complete snapshot and storage marker together. A later-page failure rolls back so retry can finish.

This owned-fork PR runs the existing four-job qualification workflow for the candidate.

Verification

• Exact main with final regressions: four fail and three controls pass. Local candidate migration/cell-scope suite: 46 pass.
• Actual production route, WorkspaceCtx lead factory, LeadDB producer and migrated SQLite: main truncates 501/1,001 leads to 500 and subsequent calls report already_migrated=500; candidate keeps all rows and tail enrichment, respects filters and preserves repeated-call behavior.
• Independent cold review additionally ran the real route on 500 and 1,501 leads (four source pages): all IDs, positions, tail receipts, filters and repeated migration passed.
• Source/test hashes and all receipts are retained in the private campaign record. All four hosted jobs passed on the cryptographically verified replacement commit.

Boundaries

No proof of a consistent snapshot while source leads change concurrently, or repair of previously completed partial migrations. HTTP auth, PostgreSQL and frontend qualification belong to the existing hosted workflow. The existing enrichment map retains its memory behavior.

Checklist

• Commit carries Rudy's DCO sign-off and a GitHub-verified SSH signature
• Scope is one workbook migration correctness fix
• Full existing four-job CI passed

Signature correction

The prior owned-fork validation PR #4 used a DCO-signed commit without a cryptographic signature. This replacement uses explicit SSH signing; GitHub commit verification is verified=true, reason valid, on 8fd7c20d99f7c59a7d624f1e582dd3a444cf940f. Its complete Git tree and source/test/diff hashes match the previously reviewed patch. The prior receipts remain preserved; this PR reruns the unchanged full workflow on the verified head. No upstream publication.

Hosted qualification

Unchanged four-job workflow passed at 8fd7c20d99f7c59a7d624f1e582dd3a444cf940f: backend SQLite 2,099 passed/134 skipped/3 deselected; PostgreSQL integrity and tenancy 18 passed; frontend lint/build and 63 Bun tests passed; mounted browser regressions 3 passed. GitHub verifies the commit signature as valid.