fix: installer stack detection, tests that can fail, proxy and port docs

- installer: decide whether the stack is extracted by the provider examples
  beside the env file, not in the working directory
- tests: assert table cells in the markdown editor pipe tests; pin the
  prompter in provider failover, the permission error on a password change
  and the built-in Bedrock config against its shipped example
- docs: state what PROXY_URL covers and which ports flows publish; name the
  cgr.dev registry of the Langfuse stack
- comments: drop history and restated code, correct those that had drifted
  from the code

Merge pull request #319 from vxcontrol/feature/next-release

Release 2.1.0: User Resources & Flow Files, Knowledge Base, ToolCall Logging, Assistant Flow Control, and Frontend Modernization