bug: CLI readAll stops reading at first empty line instead of reading to EOF

Problem

Both cli/LckJsonFmt.lean and cli/LckJsonTree.lean define a readAll helper that reads stdin line-by-line, stopping as soon as it reads an empty line:

repeat
  let line ← stdin.getLine
  if line.isEmpty then break   -- WRONG: also breaks on blank lines mid-input
  buf := buf ++ line

This means any JSON that contains a blank line (e.g., pretty-printed JSON piped from another tool, or JSON with embedded newlines before/after values) will be silently truncated.

Expected fix

Read until EOF. IO.Stream.getLine returns "" on EOF — use IO.Stream.isEof or check for EOF after each read instead of treating an empty line as the terminator. Example:

repeat
  let line ← stdin.getLine
  if (← stdin.isEof) then break
  buf := buf ++ line

References

• Flagged by AI code review on PR #8

Start with the readAll helpers in cli/LckJsonFmt.lean and cli/LckJsonTree.lean, then inspect how each CLI reads stdin. Verify the behavior with input containing a blank line and confirm that reading continues through blank lines and ends only at EOF without truncating the JSON.