fix: replace cond blocks with pattern matching and case (CSM-021)

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

test/bds/csm021_cond_pattern_match_test.exs

@@ -0,0 +1,15 @@
+defmodule BDS.CSM021CondPatternMatchTest do
+  use ExUnit.Case, async: true
+
+  describe "source-level: no cond blocks in fixed files" do
+    test "ai.ex has no cond do blocks" do
+      source = File.read!("lib/bds/ai.ex")
+      refute source =~ "cond do", "ai.ex should not contain cond do"
+    end
+
+    test "api_docs.ex has no cond do blocks" do
+      source = File.read!("lib/bds/scripting/api_docs.ex")
+      refute source =~ "cond do", "api_docs.ex should not contain cond do"
+    end
+  end
+end