fix(microprints): resolve absolute paths correctly for source viewer

- Use Path.expand(Path.join(app_root, path)) to correctly resolve both
  app files (lib/...) and blogex files (../blogex/...)
- Previously Path.join alone did not resolve '..' components, causing
  all source viewers to show the wrong file content

app/lib/firehose_web/live/microprints_live.ex

@@ -149,7 +149,7 @@ defmodule FirehoseWeb.MicroprintsLive do
     app_root = Mix.Project.project_file() |> Path.dirname()
 
     Enum.map(files, fn path ->
-      Path.join(app_root, path)
+      Path.expand(Path.join(app_root, path))
     end)
   end