feat(indexer): default contract_events ingested_at at the database

[Olasunkanmi975]

##closed #509

Summary

Moves contract_events.ingested_at to a server-authoritative database default, ensuring all ingested events receive a consistent timestamp even when application code omits the value.

Changes

• Added a database migration configuring contract_events.ingested_at with DEFAULT now().
• Updated the event store insert path to rely on the database-generated timestamp.
• Added TSDoc documenting timestamp precedence and server-authoritative behavior.
• Added tests verifying automatic timestamp generation and compatibility with explicit timestamps (if supported).

Testing

Covered:

• Insert without ingested_at.
• Insert with explicit ingested_at (if supported).
• ingested_at remains non-null.
• Existing insertion behavior is preserved.

Validation

npm test

Security

Using database-generated ingest timestamps prevents missing timestamps and reduces reliance on callers for authoritative ingest time.

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[Olasunkanmi975]

Hi maintainer, please review my work for approval

[Olasunkanmi975]

@Jagadeeshftw hi maintainer please review my pr and merge

[Jagadeeshftw]

solid change - moving ingested_at to a database default means the timestamp is always server-authoritative and can never be omitted or spoofed by application code. the migration sets DEFAULT now() at the db level, and the insert path no longer needs to supply the value. also prevents a class of bugs where a caller forgets the field and events end up with null timestamps.