Remove OpenAI: replace vector search with full-text search

[Copilot]

• Persist SQLite index to disk — search.New("search.db") writes to a file. On restart, if the DB already exists and has data, Built() returns true and indexing is skipped entirely. First startup still builds normally.
• Add synonym expansion at query time — Curated map of ~40 common Islamic terms (mercy↔forgiveness↔pardon, prayer↔salah, patience↔sabr, paradise↔jannah, etc.). expandSynonyms() automatically broadens FTS5 queries so conceptually related terms match without needing embeddings or LLM.
• Update tests — 4 new tests: TestSynonymExpansion, TestExpandSynonymsDedup, TestPersistentIndex, TestInMemoryNotBuilt. All 14 tests pass.
• Verify build and existing tests pass
• Code review and security scan — No issues found.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Remove OpenAI</issue_title>
<issue_description>Embeddings were generated using openai and we need to find a way to remove them. It might require a rethink in terms of how we're doing. Full text search. Essentially we generated embeddings so that we could do semantic search on all of the texts and then we could hand it to the llm to do rag and summarisation. But I guess there's some problems with that. One is completely tied to openai because of the way the embeddings are generated. We're also two. The searches primarily about summarisation and answers, whereas maybe a lot of people just want to see the actual results, right? So I don't know whether it means it's probably a better idea to move to full text search in a SQL database or something like that, or whether there's a way to do this without opening our eye. Or I mean, I think the answer summarisation is kind of useful book. Maybe if the core app doesn't include it that would be good. I don't know that we necessarily need a specific solution, but we need some sort of plan</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Remove OpenAI #106

---

⚡ Quickly spin up Copilot coding agent tasks from anywhere on your macOS or Windows machine with Raycast.