Interactive REPL used to always call sample_greedy_last on both the
paged and legacy KV paths, so temperature/top-k/top-p and the repetition
penalty added in the sampling module were unreachable from the CLI.
- flag() helper parses --max-tokens / --temperature / --top-k / --top-p
/ --rep-penalty / --rep-window (defaults preserve prior behavior:
temperature 0, top-p 1, penalty 1, window 512).
- pick_next() dispatches to sample_greedy_penalized only when
temperature==0 and rep_penalty>1, otherwise to sample().
- Both Qwen3/GPT-2 paths and the GptOss paged path share the same
sampler and both feed the rolling history window used for the penalty.
- Prompt input now unescapes literal "\n" so multi-turn prompts can be
typed on one line.