fix: derive pagefind language prefixes from project settings (CSM-025)

Replace hardcoded ["de/", "fr/", "it/", "es/"] with prefixes computed
from plan.blog_languages, so arbitrary language codes work correctly.
Also mark CSM-024 as fixed (done in CSM-005).

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

test/bds/csm025_hardcoded_languages_test.exs

@@ -0,0 +1,94 @@
+defmodule BDS.CSM025HardcodedLanguagesTest do
+  use ExUnit.Case, async: true
+
+  alias BDS.Generation.Pagefind
+
+  defp plan(main, languages) do
+    %{language: main, blog_languages: languages}
+  end
+
+  defp html(path), do: {path, "<p>hello</p>"}
+
+  describe "build_outputs/2 derives language prefixes from plan" do
+    test "no hardcoded language prefixes in source" do
+      source = File.read!("lib/bds/generation/pagefind.ex")
+
+      refute source =~ ~s("de/"),
+             "language prefixes must not be hardcoded — derive from plan.blog_languages"
+
+      refute source =~ ~s("fr/")
+      refute source =~ ~s("it/")
+      refute source =~ ~s("es/")
+    end
+
+    test "main language index excludes other language paths" do
+      outputs = [
+        html("index.html"),
+        html("about/index.html"),
+        html("ja/index.html"),
+        html("ko/index.html")
+      ]
+
+      result = Pagefind.build_outputs(plan("en", ["en", "ja", "ko"]), outputs)
+      main_index = Enum.find(result, fn {path, _} -> path == "pagefind/index.json" end)
+      assert main_index
+
+      {_, json} = main_index
+      decoded = Jason.decode!(json)
+      urls = Enum.map(decoded["pages"], & &1["url"])
+      assert "/index.html" in urls
+      assert "/about/index.html" in urls
+      refute "/ja/index.html" in urls
+      refute "/ko/index.html" in urls
+    end
+
+    test "non-main language index includes only its own paths" do
+      outputs = [
+        html("index.html"),
+        html("ja/index.html"),
+        html("ja/about/index.html"),
+        html("ko/index.html")
+      ]
+
+      result = Pagefind.build_outputs(plan("en", ["en", "ja", "ko"]), outputs)
+      ja_index = Enum.find(result, fn {path, _} -> path == "ja/pagefind/index.json" end)
+      assert ja_index
+
+      {_, json} = ja_index
+      decoded = Jason.decode!(json)
+      urls = Enum.map(decoded["pages"], & &1["url"])
+      assert "/ja/index.html" in urls
+      assert "/ja/about/index.html" in urls
+      refute "/index.html" in urls
+      refute "/ko/index.html" in urls
+    end
+
+    test "works with arbitrary language codes not in old hardcoded list" do
+      outputs = [
+        html("index.html"),
+        html("pt-br/index.html"),
+        html("zh-cn/index.html")
+      ]
+
+      result = Pagefind.build_outputs(plan("en", ["en", "pt-br", "zh-cn"]), outputs)
+      main_index = Enum.find(result, fn {path, _} -> path == "pagefind/index.json" end)
+      {_, json} = main_index
+      decoded = Jason.decode!(json)
+      urls = Enum.map(decoded["pages"], & &1["url"])
+      assert "/index.html" in urls
+      refute "/pt-br/index.html" in urls
+      refute "/zh-cn/index.html" in urls
+    end
+
+    test "single language blog has no exclusion prefixes" do
+      outputs = [html("index.html"), html("about/index.html")]
+
+      result = Pagefind.build_outputs(plan("en", ["en"]), outputs)
+      assert length(result) == 3
+
+      {_, json} = Enum.find(result, fn {path, _} -> path == "pagefind/index.json" end)
+      decoded = Jason.decode!(json)
+      assert length(decoded["pages"]) == 2
+    end
+  end
+end