Fix secret_mafia bug - #155

Thanks for this @MozerWang — the prompt-clarity and observation-formatting ideas here are good and worth landing. Since the branch has been idle for a while, I've picked the work up in #199, which builds on your changes with a couple of adjustments:

• Observation formatting (your "observation might be empty" fix) is adopted — actions are broadcast as readable messages instead of raw strings.
• Prompt clarity is adopted, factored into a single shared-rules helper so the four role prompts don't drift.
• Discussion parsing: your version used re.search, which captures only the first quoted segment, so "A." ... "B." would drop "B.". SecretMafia: clearer prompts, readable action broadcasts, quote-scoped discussion #199 uses re.findall + rejoin so multi-sentence speech survives, with a fallback to the full message when no quotes are present.
• Win condition: heads up that len(mafia) >= len(villagers) is algebraically identical to the existing len(mafia) >= len(alive)/2 (since alive = mafia + villagers), so it's a readability rewrite rather than a bug fix — there was no win-condition bug. SecretMafia: clearer prompts, readable action broadcasts, quote-scoped discussion #199 keeps your clearer form but notes this.

#199 verifies the game end-to-end deterministically (both win branches, quote-stripping, 12 seeded full episodes). Recommend closing this in favour of #199 once maintainers have had a look — happy to fold in any feedback.