Geo: Replicate Vulnerabilities::Export uploads

What does this MR do and why?

Add Geo SSF (self-service framework) replication and verification for the vulnerability_export_uploads partition table, so vulnerability export attachments are mirrored from the primary to secondary Geo sites alongside other upload types.

Generated with scripts/geo/generate-blob-replicator and adjusted to match the upload-partition pattern established in !229718 (merged):

• Shorten Postgres identifiers (ve_upl prefix) to fit the 63-character limit on the registry, state, and partition indexes.
• Point the upload-states foreign key at the partition table (vulnerability_export_uploads) and add a unique index on its id, since the parent uploads table has a composite primary key.
• Override Geo::VulnerabilityExportUploadRegistry.model_updated_last to :created_at because partition tables don't carry updated_at.

Replication is gated by the ops feature flag geo_vulnerability_export_upload_replication (default disabled); flipping it on for general availability is tracked separately under the parent epic.

References

• Related to #589921 (closed).
• Generator updates: !233498 (merged) (Update Geo SSF Blob Generator script).
• Parent epic: &20933 (per-upload-partition Geo replication).

How to set up and validate locally

1. Run migrations on a primary + secondary Geo setup:

   bin/rake db:migrate db:migrate:geo

2. In the primary's rails console, enable replication:

   Feature.enable(:geo_vulnerability_export_upload_replication)

3. Create a Vulnerabilities::Export with an attached file on the primary (e.g. via Vulnerabilities::Exports::ExportService or by triggering a vulnerability export from the UI).

4. On the secondary, confirm the registry row is created and synced:

   Geo::VulnerabilityExportUploadRegistry.last
   # => state: 'synced', verification_state: 'succeeded'

5. Confirm the file is present at the secondary's upload path and that verification_checksum matches the primary's checksum.

6. Optionally, force a re-verification:

   Geo::VulnerabilityExportUploadRegistry.last.verification_pending!

MR acceptance checklist

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