refactor: replace inline path utilities with path package

basename, dirname, and slugFromFilename now delegate to the path package.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.lux

@@ -1,5 +1,6 @@
 import markdown
 import frontmatter
+import path
 
 type SiteConfig =
     | SiteConfig(String, String, String, String, String, String, String)
@@ -145,7 +146,7 @@ fn teSection(e: TagEntry): String =
     TagEntry(_, _, _, _, s) => s,
 }
 
-fn slugFromFilename(filename: String): String = if String.endsWith(filename, ".md") then String.substring(filename, 0, String.length(filename) - 3) else filename
+fn slugFromFilename(filename: String): String = path.stripExtension(filename)
 
 fn formatDate(isoDate: String): String = {
     if String.length(isoDate) < 10 then isoDate else {
@@ -157,17 +158,9 @@ fn formatDate(isoDate: String): String = {
 }
 }
 
-fn basename(path: String): String =
-    match String.lastIndexOf(path, "/") {
-    Some(idx) => String.substring(path, idx + 1, String.length(path)),
-    None => path,
-}
+fn basename(p: String): String = path.basename(p)
 
-fn dirname(path: String): String =
-    match String.lastIndexOf(path, "/") {
-    Some(idx) => String.substring(path, 0, idx),
-    None => ".",
-}
+fn dirname(p: String): String = path.dirname(p)
 
 fn sortInsert(sorted: List<Page>, item: Page): List<Page> = insertByDate(sorted, item)