feat: Add default input handling and file reading for Day 2 solution

fix: Resolve compilation errors in Day2 solution

lib/advent_code2024/solutions/day02/day2.ex

@@ -3,12 +3,24 @@ defmodule AdventCode2024.Solutions.Day2 do
   Solution for Day 2: Red-Nosed Reports
   """
 
+  @default_input "priv/inputs/day02/input.txt"
+
   @doc """
   Analyzes reactor reports to count how many are safe according to the rules.
   Returns {:ok, count} for valid input or {:error, reason} for invalid input.
   """
+  def solve(input \\ @default_input)
+  def solve(""), do: {:error, :no_valid_reports}
   def solve(input) when is_binary(input) and input != "" do
-    lines = String.split(input, "\n", trim: true)
+    case File.read(input) do
+      {:ok, content} -> solve_content(content)
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp solve_content(""), do: {:error, :no_valid_reports}
+  defp solve_content(content) when is_binary(content) and content != "" do
+    lines = String.split(content, "\n", trim: true)
 
     with {:ok, reports} <- parse_reports(lines) do
       safe_count = Enum.count(reports, &safe_report?/1)
@@ -16,8 +28,6 @@ defmodule AdventCode2024.Solutions.Day2 do
     end
   end
 
-  def solve(""), do: {:error, :no_valid_reports}
-
   defp parse_reports(lines) do
     reports = Enum.map(lines, &parse_line/1)