#28 Allow the browser-test port to be set with TEST_PORT

Lets several checkouts run npm test at the same time. The default stays 8897.

🤖 Generated with Claude Code

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Summary by cubic

Lets several checkouts run npm test at the same time by setting the browser-test port with the TEST_PORT environment variable; the default stays 8897. The suite now also fails fast instead of testing another server's files when its port is already taken. The contributing docs mention the new option.

Summary by CodeRabbit

• Documentation

  • Updated browser-test documentation to explain that the test server port can be configured with TEST_PORT.
  • Clarified that the default test server port remains 8897.

• Tests

  • Browser tests now consistently use the configured TEST_PORT value when starting the test server and connecting to it.
  • Existing support for configuring the Python executable remains unchanged.