fix: resolve clippy empty line after doc comment warning

Include empty line in struct documentation to satisfy clippy lint.

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Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: jrollin

src/content/common_word.rs

@@ -1,6 +1,6 @@
 /// Common word training support for typing practice
 /// 500 most common words per language with frequency weighting
-
+///
 /// A single common word with frequency data
 #[derive(Debug, Clone)]
 pub struct Word {