Add PostgreSQL GIN full-text search index on shipment description for performant keyword search

[shakurJJ]

Summary

The case-insensitive contains search on the description field uses a sequential scan. At scale this degrades to a full table scan on every search request. A PostgreSQL tsvector column with a GIN index would make text search performant and support prefix/stemming queries.

Location

prisma/schema.prisma — add a generated tsvector column with GIN index via a raw migration
src/modules/shipments/shipments.service.ts — switch findAll() search to use to_tsquery()

Expected Behaviour

1. Add a migration that adds a description_search tsvector GENERATED ALWAYS AS (to_tsvector('english', coalesce(description, ''))) STORED column to shipments and creates a CREATE INDEX CONCURRENTLY shipments_description_search_idx ON shipments USING GIN (description_search).
2. In findAll(), replace the { contains: search, mode: 'insensitive' } clause with a prisma.$queryRaw that uses description_search @@ plainto_tsquery('english', ${search}).
3. Keep the contains fallback for referenceNumber exact match.

Acceptance Criteria

• Text search uses the GIN index (confirmed via EXPLAIN ANALYZE in migration tests)
• Migration runs without locking the table (uses CONCURRENTLY)
• Search results are unchanged from the user's perspective
• The feature works with the existing search query parameter

[Tekprecious]

@Tekprecious has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I have experience for this and have reviewed the code; I can submit a PR within 24hrs.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Tekprecious to this issue.