fix(search): link results to book detail page and add cover thumbnails

Search results navigated to /bookshelf with no filters instead of the
selected book's page. Results now link to /media/:id and display cover
thumbnails, with cover URLs resolved server-side via ResolveMediaURL.
Removes the dead selectedBook localStorage plumbing.

internal/handlers/media.go

@@ -1791,6 +1791,10 @@ func (mh *MediaHandler) SearchMediaItems(c *echo.Context) error {
 			"results": []interface{}{},
 		})
 	}
+	for i := range results {
+		resolved := utils.ResolveMediaURL(results[i].LibraryID, results[i].CoverImagePath)
+		results[i].CoverImagePath = pgtype.Text{String: resolved, Valid: resolved != ""}
+	}
 	return c.JSON(http.StatusOK, results)
 }