feat(email-marketing): add indexes to segment_rules table

[Moh-dakai]

Summary

segment_rules had no indexes beyond the primary key, forcing sequential scans on every query as the table grows. This adds targeted indexes covering the
table's actual query paths and creates a migration to apply them to existing databases.

Changes

src/email-marketing/entities/segment-rule.entity.ts

• Added @Index import from typeorm
• Added three class-level @Index decorators (see index strategy below)

src/migrations/1803000000000-add-segment-rule-indexes.ts

• New migration using CREATE INDEX IF NOT EXISTS — safe to run on databases that already have partial indexes from a previous deploy
• down() drops all three indexes via DROP INDEX IF EXISTS

Index strategy

┌───────────────────────────────────┬──────────────────┬───────────────────────────────────┬────────────────────────────────────────────────────────────────┐
│ Index │ Columns │ Type │ Query path covered │
├───────────────────────────────────┼──────────────────┼───────────────────────────────────┼────────────────────────────────────────────────────────────────┤
│ IDX_segment_rules_segmentId │ segmentId │ Single │ FK lookup; all "load rules for segment" queries; ON DELETE │
│ │ │ │ CASCADE resolution │
├───────────────────────────────────┼──────────────────┼───────────────────────────────────┼────────────────────────────────────────────────────────────────┤
│ IDX_segment_rules_segmentId_order │ segmentId, order │ Composite │ WHERE segmentId = $1 ORDER BY order — resolved in a single │
│ │ │ │ index scan, no sort step │
├───────────────────────────────────┼──────────────────┼───────────────────────────────────┼────────────────────────────────────────────────────────────────┤
│ IDX_segment_rules_deletedAt │ deletedAt │ Partial (WHERE deletedAt IS NULL) │ Soft-delete filter; only indexes active rows, keeping the │
│ │ │ │ index small │
└───────────────────────────────────┴──────────────────┴───────────────────────────────────┴────────────────────────────────────────────────────────────────┘

field and operator were intentionally left without standalone indexes — they are low-cardinality enum columns always fetched as part of a segmentId lookup, so
standalone indexes would add write overhead with no meaningful read benefit.

Testing

• TypeScript type-check passes (tsc --noEmit)
• Migration timestamp 1803000000000 is unique across all existing migrations
• No pre-existing IDX_segment_rules_* names in any other migration or the baseline schema

closes #1236

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[RUKAYAT-CODER]

Well done on the job done so far!
Kindly fix workflow to pass

[Moh-dakai]

Well done on the job done so far! Kindly fix workflow to pass

Thank you very much, i've resolved the workflow issue and look forward to working with you on many more projects to come.

[RUKAYAT-CODER]

Thank you for contributing to the project