Make JA4s have names + drop unused index

[skyfallwastaken]

Summary of the problem

JA4s don't have names :(

Describe your changes

Make the admin heartbeats endpoint return JA4 fingerprints and names.

Screenshots / Media

N/A

[greptile-apps]

Greptile Summary

This PR adds JA4 names to the admin heartbeats response. The main changes are:

• Adds a nullable name column to ja4s.
• Returns JA4 data as an object with fingerprint and name.
• Updates admin API tests and OpenAPI docs for the new response shape.
• Drops unused heartbeat indexes through a new migration.

Confidence Score: 4/5

The API response shape and schema updates are straightforward, with one rollback-path issue that should be corrected to avoid schema drift.

The changed request specs and docs cover the intended JA4 response update, and the remaining concern is isolated to migration rollback behavior rather than normal forward execution.

db/migrate/20260620232900_drop_unused_heartbeat_indexes.rb

T-Rex Logs

What T-Rex did

• Reviewed the base controller response, which returned HTTP 200 and a JA4 heartbeat string when JA4 is present and null when absent.
• Verified the head controller response after the change, which returns HTTP 200 and a JA4 heartbeat object with fingerprint and name when JA4 is present, while the no-JA4 case remains null.
• Inspected logs to confirm the presence of the two controller responses and the JA4 heartbeat values across states.

_{Ran code and verified through T-Rex}

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
db/migrate/20260620232900_drop_unused_heartbeat_indexes.rb:23-27
**Rollback adds index**

The `down` path recreates `index_heartbeats_on_last_language_user_id`, but the schema before this migration did not contain that index. Rolling this migration back would leave the database with a new partial index that was not part of the previous schema, which can cause schema drift and an unexpected large index build on `heartbeats` during rollback.

_{Reviews (1): Last reviewed commit: "Update Swagger specs" | Re-trigger Greptile}