fix(docs): resolve all broken rustdoc intra-doc links

Fix direct path references for in-scope items (GammaStrategy,
CompletedTrial) and convert feature-gated items to plain backtick
formatting so docs build cleanly without --all-features.

src/study/mod.rs

@@ -225,7 +225,7 @@ where
     ///
     /// This is the most general constructor — all other constructors
     /// delegate to this one. Use it when you need a non-default storage
-    /// backend (e.g., [`JournalStorage`](crate::storage::JournalStorage)).
+    /// backend (e.g., `JournalStorage`).
     ///
     /// # Arguments
     ///