WordCountService edge cases: adjacent block elements and '..' path names #1610

(1) InnerText concatenation likely undercounts words for adjacent block elements with no whitespace (<p>one</p><p>two</p>). (2) relative.StartsWith("..") wrongly rejects legitimate names like ..notes/a.html. (3) ResolvePath duplicates HomeController's path-join logic. Add tests and fix.

Found during review of #1267; intentionally kept out of that PR.