gofmt the kiwix client and rewrite test

PR #41 and #44 landed these two files unformatted, so the gofmt gate that
PR #12 added to `make test` failed as soon as both were on one branch.
Struct-tag and comment alignment only, no semantic change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

internal/kiwix/client.go

@@ -82,7 +82,7 @@ type rss struct {
 		Description struct {
 			Inner string `xml:",innerxml"`
 		} `xml:"description"`
-		WordCount   string `xml:"wordCount"`
+		WordCount string `xml:"wordCount"`
 	} `xml:"channel>item"`
 }