feat: add search_indexes parameter to ProcessChunks and ProcessFileEmbedding (#856)

[pyramation]

Summary

Adds search_indexes parameter to the ProcessChunks node type definition and the ProcessFileEmbedding chunks sub-config in the node type registry.

search_indexes: {
  type: 'array',
  items: { type: 'string', enum: ['fulltext', 'bm25', 'trigram'] },
  default: ['fulltext']
}

This enables hybrid RAG workflows — keyword search (tsvector/BM25/trigram) alongside vector similarity search on the chunks table's content column.

The default [\"fulltext\"] is centralized here in the parameter_schema and applied by table_module normalization before reaching the SQL generator.

Review & Testing Checklist for Human

• Verify search_indexes property matches the SQL column type (jsonb array of strings)
• Confirm default ['fulltext'] aligns with the SQL column default '[\"fulltext\"]'::jsonb

Notes

• Companion to constructive-io/constructive-db#1164 (SQL implementation)
• Closes constructive-io/constructive-planning#856 (together with the DB PR)

Link to Devin session: https://app.devin.ai/sessions/2b5a29d83d3f478e8d3d972653b4879c
Requested by: @pyramation

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