WIP: Add backfill_program_certificate_titles management command

[zamanafzal]

What are the relevant tickets?

https://github.com/mitodl/hq/issues/11938

Description

Issued program certificates freeze their "Certificate Title" (product_name) into the Wagtail page revision in effect at issue time (ProgramCertificate.certificate_page_revision), and the display path reads certificate_page_revision.as_object().product_name. So editing the live "Certificate Title" in the CMS does not update certificates already issued — they keep their old frozen title until a one-time backfill is run.

This adds a backfill_program_certificate_titles management command (workstream 1 of hq#11938, follow-up to hq#11907 / #3695) that rewrites each issued program certificate's frozen product_name to the live CMS page value.

python manage.py backfill_program_certificate_titles \
    (--program <readable_id> [--program <readable_id> ...] | --all-programs) \
    [--commit]

Behavior & safety

• Dry-run by default — reports planned changes; --commit is required to write.
• Mode validation — exactly one of --program (repeatable) / --all-programs; neither or both raises CommandError, so a bare run touches nothing.
• Placeholder/empty guard — skips any program whose live title is empty or still a "PLACEHOLDER - " default; placeholder text is never stamped onto real certificates.
• Idempotent — revisions already matching the live title are reported [skipped]; a second --commit run is a no-op.
• Distinct-revision dedup — certs issued at the same page revision share one Revision row, so each shared revision is edited once (report shows (N certs)).
• Tolerant skips (never crash) — unknown readable_id, missing CMS page, missing certificate page, and null-revision (revoked) certs are reported and skipped.
• Per-program writes run inside transaction.atomic(); a final Summary: line tallies programs processed/skipped, revisions changed, and certs affected.

Write strategy

Edits the existing Revision.content["product_name"] in place (per design): simplest, fewest writes, fixes all certs sharing a revision at once. Trade-off — the page's revision-history view will retroactively show the corrected title, which is acceptable for a one-time correction.

Test plan

• --commit rewrites frozen product_name to the live title (asserted via the display path revision.as_object().product_name)
• Dry-run (default) makes no DB writes and reports the planned change
• Idempotent: second --commit reports zero changes
• Placeholder / empty live title → program skipped, no writes
• Null-revision (revoked) cert → not touched
• Shared revision: multiple certs → single edit, all updated
• Mode validation: neither flag → CommandError; both flags → CommandError
• --all-programs processes clean programs and skips placeholder / page-less ones
• Unknown --program readable_id reported and skipped; other programs still processed
• 14 tests pass; ruff format + ruff check clean

[github-actions]

OpenAPI Changes

Show/hide ## Changes for v0.yaml:

## Changes for v0.yaml:
2 changes: 1 error, 0 warning, 1 info
error	[api-path-removed-without-deprecation] at base/openapi/specs/v0.yaml
	in API POST /api/v0/b2b/manager/organizations/{parent_lookup_organization}/contracts/{id}/codes/send_test_email/
		api path removed without deprecation

info	[api-schema-removed]
	in components/schemas
		removed the schema `SendTestEmailRequest`



## Changes for v1.yaml:
2 changes: 1 error, 0 warning, 1 info
error	[api-path-removed-without-deprecation] at base/openapi/specs/v1.yaml
	in API POST /api/v0/b2b/manager/organizations/{parent_lookup_organization}/contracts/{id}/codes/send_test_email/
		api path removed without deprecation

info	[api-schema-removed]
	in components/schemas
		removed the schema `SendTestEmailRequest`



## Changes for v2.yaml:
2 changes: 1 error, 0 warning, 1 info
error	[api-path-removed-without-deprecation] at base/openapi/specs/v2.yaml
	in API POST /api/v0/b2b/manager/organizations/{parent_lookup_organization}/contracts/{id}/codes/send_test_email/
		api path removed without deprecation

info	[api-schema-removed]
	in components/schemas
		removed the schema `SendTestEmailRequest`

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