fix(postgres): stop rebuilding every BM25 index on startup

[walcz-de]

Problem

ensureBM25IndexConfig builds the expected string as text_config='<cfg>' (quoted) and looks for it in the output of pg_get_indexdef(). PostgreSQL renders the option unquoted:

BM25 index text_config differs, recreating index="idx_documents_pprls_docs_bm25" want="simple"
current_def="CREATE INDEX … USING bm25 (full_text) WITH (text_config=simple)"

The check can never match, so every startup drops and rebuilds every BM25 index, even when nothing changed. On our instance (~90 collections) that meant ~90 index rebuilds per start: 186 of these log lines over two restarts. It also hides the one case the check exists for, a real config change.

Fix

Extract the text_config value from the index definition with a small regex that accepts the quoted and the unquoted form (including schema-qualified configs such as public.de_en), and compare it case-insensitively. A different config still drops the index and triggers the rebuild, as before.

The bug came in with the env-configurable text_config (#52, ours).

Tests

rag/engine/postgres_bm25_config_test.go, pure function, no database needed:

• unquoted form from pg_get_indexdef → match
• quoted form → match
• schema-qualified custom config → match
• different config → no match (rebuild still happens)
• no text_config at all → no match

go test ./rag/engine/ -args -ginkgo.focus=bm25IndexHasTextConfig: 5 passed. Without the fix the new tests do not build (the helper is new). gofmt, go vet clean.

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