refactor(fts): address PR #488 review concerns

- Extract isPureTextRelevance() private static method to replace the
  7-clause inline boolean in searchDocuments
- Guard long→int cast in relevanceSortedPageFromSql to prevent silent
  overflow at page ≥43M (CWE-190)
- resolvePersonName now uses the typed API client (createApiClient)
  instead of raw fetch, aligning with project conventions
- Update DocumentServiceTest stubs to match new FTS path (findFtsPageRaw
  + findAllById instead of findAllMatchingIdsByFts)
- Rewrite page.server.spec.ts person-name tests to mock via path-based
  API dispatch, matching the new api.GET call site

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

frontend/src/routes/documents/+page.server.ts

@@ -5,14 +5,17 @@ import type { components } from '$lib/generated/api';
 
 const UUID_RE = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
 
-async function resolvePersonName(id: string, fetch: typeof globalThis.fetch): Promise<string> {
+async function resolvePersonName(
+	id: string,
+	api: ReturnType<typeof createApiClient>
+): Promise<string> {
 	if (!UUID_RE.test(id)) return '';
 	try {
-		const res = await fetch(`/api/persons/${id}`);
-		if (!res.ok) return '';
-		const person = await res.json();
-		return person.displayName ?? '';
-	} catch {
+		const result = await api.GET('/api/persons/{id}', { params: { path: { id } } });
+		if (!result.response.ok) return '';
+		return result.data?.displayName ?? '';
+	} catch (e) {
+		console.error('[resolvePersonName] failed for id', id, e);
 		return '';
 	}
 }
@@ -70,7 +73,7 @@ export async function load({ url, fetch }) {
 					}
 				}
 			}),
-			Promise.all([resolvePersonName(senderId, fetch), resolvePersonName(receiverId, fetch)])
+			Promise.all([resolvePersonName(senderId, api), resolvePersonName(receiverId, api)])
 		]);
 	} catch {
 		return {