fix(fts): count query terms, not dictionary terms, in conjunctive queries

[zahariash]

This work was produced with the help of language models.

Fixes #117.

With conjunctive := true, QUERY_FTS_INDEX accepted a document when it matched as many dictionary terms as the query had terms. A wildcard expands to several dictionary terms, so foo* qux accepted a document with foobar and foobaz but no qux and rejected one containing all three, and foo fo* rejected a document containing only foo.

Fix. Query terms are deduplicated after stemming. Each matched dictionary term records which query terms it satisfies, and a document passes the conjunctive check when every query term is covered by one of its terms. Scores are unchanged: every matched dictionary term still contributes one edge per document. Single-threaded instruction counts on 1M documents are within noise of main for plain, wildcard, multi-term and conjunctive queries.

Tests. wildcard.test gains a conjunctive case: foo* qux returns only the documents with qux, foo fo* only the document with foo, the same wildcard query without conjunctive returns all four documents, foobar qux behaves as before, a repeated term (qux qux) counts once, and a wildcard matching nothing (zzz* foo) returns no rows. It fails on main and passes here. FTS extension tests: no new failures.