Resolves#36365
The v4.76.0 checksum change (#34097) reordered the fields hashed into
`Software.ComputeRawChecksum` for non-`apps` sources, so software rows
created before the upgrade no longer matched re-ingested rows and got
duplicated (same name/version/source, split host counts).
- Make `ComputeRawChecksum` the sole source of truth and delete the
drifted parallel SQL checksum formula that caused the mismatch.
- Add `ReconcileSoftwareChecksums`, a one-shot migration that merges
existing duplicates onto the canonical row (batched host_software
repointing) and logs each merge. Runs once after startup; re-run with
`fleetctl trigger --name software_checksum_migration`
Juan Fernandez
e529d97897