Add vector index options and Spark DDL scaffolding

Parent: #19094
Related: #18676

## Summary
Add the Spark DDL and option surface for vector indexes.

## Scope
- `CREATE INDEX ... USING VECTOR`
- vector option parsing and validation
- metric and quantizer options
- `vector.rabitq.total_bits`
- lifecycle entry points for create/drop/show/validation

## Acceptance Criteria
- option surface is defined and validated
- invalid configurations fail early
- DDL scaffolding is separated from payload and execution logic

Start by reading parent issue #19094 and related issue #18676 to establish the intended vector-index design and boundaries. Use the stated scope and acceptance criteria as the completion checklist: Spark DDL and options are defined and validated, invalid configurations fail early, and lifecycle scaffolding remains separate from payload and execution logic.

Written by the indexing model from the issue text.