Scope

What's changed:

• Extended createIndex schema helper to accept composite indexes
• Added migration to create index on directus_revisions(collection, item, version)

Potential Risks / Drawbacks

• Migration may take time on large directus_revisions tables (uses attemptConcurrentIndex to minimize locking)
• MySQL limited to 16 columns per composite index (documented in JSDoc)

Tested Scenarios

• Unit tests for composite index SQL generation on all dialects
• Blackbox test for composite index functionality

Checklist

• Added or updated tests
• Documentation PR created here or not required
• OpenAPI package PR created here or not required

Fixes #26272