enhancement: make code_vector mapping conditional when ENABLE_DENSE_VECTORS is false

[kapral18]

Problem

The index mapping always defines code_vector as an indexed dense_vector field:

• index: true

Even when ENABLE_DENSE_VECTORS is disabled, this mapping can still increase index overhead (storage, indexing CPU) and potentially require extra cluster resources.

Where in code

• src/utils/elasticsearch.ts in createIndex() mapping for code_vector.

Suggested fix

Options:

1. Only include the code_vector field mapping when ENABLE_DENSE_VECTORS=true.
2. Keep the field but set index: false unless enabled.

Notes

This is a mapping change; deployments will need a clean reindex to pick it up.

Test plan

• Unit test for createIndex mapping generation (mock client) verifying code_vector is omitted or non-indexed when disabled.