feat(migration): drop legacy unique index on folders table

[jzunigax2]

What

Drop the legacy unique index folders_plainname_parentid_key from the folders table, now that the replacement index folders_parentuuid_plainname_unique has been deployed in PR #882.

Why

1. Index is no longer used

The legacy index has not been scanned since 2026-01-07, when the optimized idx_folders_user_parentuuid_plainname_not_deleted_removed index was introduced.

Metric	Value
Last scanned	2026-01-07 (12+ days ago)
Size	5,940 MB
Historical scans	2.6B
Historical tuple reads	88T
Historical tuple fetches	3,115

2. Redundant uniqueness enforcement

With PR #882 merged, we now have a proper unique constraint on (parent_uuid, plain_name) that:

• Aligns with application code (findByNameAndParentUuid)
• Uses optimal column order (high-cardinality column first)

The legacy index on (plain_name, parent_id) is now fully redundant.

3. Write performance impact

Despite not being scanned, the index is still maintained on every write operation.

4. Disk space recovery

Dropping this index reclaims 5,940 MB of disk space.

How

Migration uses DROP INDEX CONCURRENTLY to avoid table locks:

DROP INDEX CONCURRENTLY IF EXISTS folders_plainname_parentid_key;

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

This PR is stale because it has been open for more than 15 days with no activity.

[github-actions]

This PR is stale because it has been open for more than 15 days with no activity.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sg-gs]

Running migration @jzunigax2

[sg-gs]

Migration run @jzunigax2

Sequelize CLI [Node: 22.16.0, CLI: 6.6.3, ORM: 6.37.7]

Loaded configuration file "src/config/sequelize.js".
Using environment "production".
== 20260320042454-drop-legacy-unique-index-folders-plainname-parentid: migrating =======
== 20260320042454-drop-legacy-unique-index-folders-plainname-parentid: migrated (3.357s)

Done in 5.68s.