Fix kiwix proxy 502ing on article links with non-ASCII titles

Sinatra decodes a route's splat before handing it to the block, so an
article link like /kiwix/content/wikipedia/Dlhé_diely arrived as raw
UTF-8, not percent-encoded. URI#path= rejects that outright
(URI::InvalidComponentError) rather than escaping it, which .proxy's
rescue turned into a silent nil -> every article link 502'd, while the
search results page linking to them worked fine (its own path,
/kiwix/search, is plain ASCII).

test/test_kiwix.rb

@@ -45,4 +45,29 @@ class KiwixTest < Minitest::Test
   def test_proxy_returns_nil_when_nothing_is_listening
     assert_nil Maptool::Kiwix.proxy("http://127.0.0.1:1", "/kiwix/search", "", open_timeout: 1)
   end
+
+  # A path with non-ASCII characters, e.g. an article title like
+  # "/kiwix/content/wikipedia/Dlhé_diely" — exactly what Sinatra's splat
+  # hands .proxy for a real article link, already URL-*decoded*. Used to
+  # raise URI::InvalidComponentError (caught, so this returned nil — every
+  # article link 502'd) since URI#path= rejects raw UTF-8 bytes outright
+  # instead of escaping them.
+  def test_proxy_escapes_non_ascii_characters_in_the_path
+    server = TCPServer.new("127.0.0.1", 0)
+    port = server.addr[1]
+    request_line = nil
+    thread = Thread.new do
+      client = server.accept
+      request_line = client.gets
+      client.print("HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 0\r\n\r\n")
+      client.close
+    end
+
+    response = Maptool::Kiwix.proxy("http://127.0.0.1:#{port}", "/kiwix/content/wikipedia/Dlhé_diely", "")
+    thread.join
+    server.close
+
+    assert_equal "GET /kiwix/content/wikipedia/Dlh%C3%A9_diely HTTP/1.1\r\n", request_line
+    assert_equal "200", response.code
+  end
 end