fix(interactive): process every stdin line and resolve on EOF

[Mohammed Alkindi (MohammedAlkindi)]

In stdin mode, processRequests called question() once per request, so input that arrived while a request was running was lost:

• a line typed or pasted during a request was dropped, and the rest of a multi-line paste too;
• EOF (Ctrl+D, or the end of a pipe) left the promise pending, or rejected it with readline was closed if it came mid-request.

The Python port already reads every line and stops at EOF. The loop now iterates the readline interface, which buffers lines and ends on EOF. It prompts only while the interface is open and not paused, so readline still stops reading stdin when its line buffer fills.

The file-reading branch is untouched, so this is independent of #435.

The new test/interactive-stdin.test.ts swaps process.stdin for a stream it controls. All 5 tests fail on main; npm test gives 118 passed on Node 24.18. CI runs only build-all, not npm test.