refactor(db): typed query helpers, shared test FormData helper

Replace raw db.execute tuple casts with queryRows/rowsFrom/execResult/
affectedRows helpers from lib/db, drop redundant mysql2 casts on typed
query builders, and centralize per-test fakeForm into test/fake-form.
Update db mocks in tests so helpers resolve against mocked execute.

src/actions/messenger.ts

@@ -297,10 +297,7 @@ export async function removeFriendship(formData: FormData): Promise<void> {
 							),
 						);
 
-					return Number(
-						(result as unknown as [{ affectedRows: number }])[0]
-							?.affectedRows ?? 0,
-					);
+					return Number(result[0]?.affectedRows ?? 0);
 				});
 
 				outcome = deleted > 0 ? "removed" : "not_found";