feat(pdp): add AddRoots tracking endpoints

[rvagg]

From #530 for the synapse branch.

Summary is that AddRoots is currently a blind operation, you throw it over to Curio and cross your fingers. This is unlike CreateProofSets where you get a Location header response which points you to a URL which will give you both the transaction to watch on chain and the status as far as Curio is concerned.

This adds similar capabilities for AddRoots; you get a Location header and the ability to track an AddRoots operation. It also fills in the stub implementation of handleGetProofSetRoot which is a generalised "get me root info" endpoint.

This is being used to do the full onboarding lifecycle from the client end, allowing the end-user to track the transaction both on chain and getting Curio confirmation that it agrees it's landed.

feat(pdp): add transaction tracking for root additions

- Add Location header to root addition response with tx hash
- Add GET /proof-sets/{id}/roots/added/{txHash} endpoint for status checks
- Implement handleGetProofSetRoot for retrieving root details
- Return confirmed root IDs after transaction confirmation

and (bugfix):

fix(pdp): use lowercase transaction hashes consistently in database operations

and:

fix(pdp): retain root addition records to prevent 404s on status queries 

Previously, pdp_proofset_root_adds records were deleted after processing,
causing clients to receive 404 errors when querying transaction status
after successful root additions. This created a poor UX as clients couldn't
verify transaction outcomes if they queried too late.

This change aligns root addition tracking with proof set creation by:
- Adding roots_added column to mark processed records instead of deleting
- Updating watcher to UPDATE instead of DELETE when processing completes
- Including roots_added status in API response for client visibility

The fix ensures transaction status remains queryable indefinitely while
maintaining backward compatibility. Existing records will be processed
normally with roots_added=FALSE by default.

API enhancement: /pdp/proof-sets/{id}/roots/added/{txHash} now includes
"rootsAdded" field indicating if roots were fully processed.

[rvagg]

@LexLuthr I removed the AuthService stuff from here so it should be good for review now

[ZenGround0]

#530 LGTM for landing in main, once that review is responded to and this is rebased I'll look this one over one more time.