feat(TRUEREF-0006): implement SQLite FTS5 full-text search engine

- BM25 ranking via SQLite FTS5 bm25() function
- Query preprocessor with wildcard expansion and special char escaping
- Library search with composite scoring (name match, trust score, snippet count)
- Trust score computation from stars, coverage, and source type
- Response formatters for library and snippet results

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/server/search/query-preprocessor.ts

@@ -0,0 +1,34 @@
+/**
+ * Query preprocessor for FTS5 search queries.
+ *
+ * Normalizes raw user input into an FTS5-compatible MATCH expression
+ * with prefix wildcard expansion on the last token.
+ */
+
+/**
+ * Preprocess a raw search query string for FTS5 MATCH.
+ *
+ * Steps:
+ * 1. Trim and normalize internal whitespace.
+ * 2. Strip FTS5 grouping characters `(` and `)` that would cause parse errors.
+ * 3. Append a prefix wildcard `*` to the last token when it is >= 3 characters
+ *    and does not already end with `*`. This gives a "typing as you go" feel.
+ */
+export function preprocessQuery(raw: string): string {
+	// 1. Trim and collapse whitespace.
+	let q = raw.trim().replace(/\s+/g, ' ');
+
+	// 2. Remove parentheses (not valid in simple FTS5 queries without explicit operators).
+	q = q.replace(/[()]/g, ' ').replace(/\s+/g, ' ').trim();
+
+	if (!q) return q;
+
+	// 3. Add prefix wildcard to the last token.
+	const tokens = q.split(' ');
+	const lastToken = tokens.at(-1) ?? '';
+	if (lastToken.length >= 3 && !lastToken.endsWith('*')) {
+		tokens[tokens.length - 1] = lastToken + '*';
+	}
+
+	return tokens.join(' ');
+}