Support running x86_64 Docker from other platforms

Now that my primary machine has an M1 processor, I need to specify a
different architecture. This shouldn't have any effect at runtime,
other than being a bit more specific.

It is a bit slower to do the emulation, so I'm also making the
Capybara timeout adjustable via environment variable.

Author: shepmaster

tests/spec/spec_helper.rb

@@ -58,7 +58,7 @@
 Capybara.default_driver = Capybara.javascript_driver = :firefox
 Capybara.app_host = "http://#{ADDRESS}:#{PORT}"
 Capybara.run_server = false
-Capybara.default_max_wait_time = 5
+Capybara.default_max_wait_time = ENV.fetch('CAPYBARA_WAIT', 5).to_f
 Capybara.automatic_label_click = true
 
 Capybara::Screenshot.register_driver(:firefox) do |driver, path|

ui/src/sandbox.rs

@@ -439,6 +439,8 @@ macro_rules! docker_command {
 fn basic_secure_docker_command() -> Command {
     let mut cmd = docker_command!(
         "run",
+        "--platform",
+        "linux/amd64",
         "--detach",
         "--cap-drop=ALL",
         // Needed to allow overwriting the file