style: apply gofmt across Go sources

Repo-wide gofmt sweep: const-block alignment, doc-comment spacing,
statement-after-brace fix in media.go, trailing blank lines. No
semantic changes — whitespace-insensitive diff is empty for every
file in this commit.

internal/sync/kepub_cfi_converter_test.go

@@ -108,12 +108,12 @@ func createTestEPUB(t *testing.T, dir, name, ch1Content, ch2Content string) stri
 	w := zip.NewWriter(f)
 
 	files := map[string]string{
-		"mimetype":            "application/epub+zip",
+		"mimetype":               "application/epub+zip",
 		"META-INF/container.xml": containerXML,
-		"OEBPS/content.opf":   contentOPF,
-		"OEBPS/nav.xhtml":     navXHTML,
-		"OEBPS/chapter1.xhtml": ch1Content,
-		"OEBPS/chapter2.xhtml": ch2Content,
+		"OEBPS/content.opf":      contentOPF,
+		"OEBPS/nav.xhtml":        navXHTML,
+		"OEBPS/chapter1.xhtml":   ch1Content,
+		"OEBPS/chapter2.xhtml":   ch2Content,
 	}
 
 	mimetype, _ := w.Create("mimetype")