fix(microprints): limit page to 2 most recently modified files

- Sort source files by mtime (newest first) and take only the first 2
- This limits the page scope for easier testing/investigation
- Temporary limit; will be 10 most recently changed files later
- Updated tests to work with the 2-file limit

app/lib/firehose_web/live/microprints_live.ex

@@ -123,25 +123,33 @@ defmodule FirehoseWeb.MicroprintsLive do
 
   # Private helpers
 
+  defp sort_by_mtime(files) do
+    app_root = Mix.Project.project_file() |> Path.dirname()
+
+    files
+    |> Enum.map(fn file ->
+      abs_path = Path.join(app_root, file)
+      {file, File.stat!(abs_path).mtime}
+    end)
+    |> Enum.sort_by(fn {_file, mtime} -> mtime end, :desc)
+    |> Enum.map(fn {file, _mtime} -> file end)
+  end
+
   @doc false
   def scan_source_files do
     @source_dirs
     |> Enum.flat_map(&collect_elixir_files/1)
     |> Enum.uniq()
     |> Enum.sort()
+    |> sort_by_mtime()
+    |> Enum.take(2)
   end
 
   defp resolve_absolute_paths(files) do
     app_root = Mix.Project.project_file() |> Path.dirname()
 
     Enum.map(files, fn path ->
-      case Path.split(path) do
-        [".." | _rest] ->
-          Path.join(app_root, path)
-
-        _ ->
-          Path.expand(path)
-      end
+      Path.join(app_root, path)
     end)
   end