docs: add role-play provider evaluation

[JOY (JOY)]

Summary

• Add docs/design/52-llm-role-play-provider-evaluation.md for Alibaba Qwen-Character and similar role-play providers.
• Update architecture, AI NPC roadmap, alpha decision register, GitBook summary, and ROADMAP to keep provider experiments behind api.dos.ai.
• Create and link backlog issue Benchmark role-play model providers behind api.dos.ai #249 for a future provider bake-off.

Verification

• git diff --check
• git diff --cached --check
• npx markdownlint-cli2 ROADMAP.md docs/ARCHITECTURE.md docs/SUMMARY.md docs/design/37-ai-npc-backend-client-roadmap.md docs/design/38-alpha-design-decision-register.md docs/design/52-llm-role-play-provider-evaluation.md
• rg "[\u2013\u2014]" ROADMAP.md docs\SUMMARY.md docs\ARCHITECTURE.md docs\design\37-ai-npc-backend-client-roadmap.md docs\design\38-alpha-design-decision-register.md docs\design\52-llm-role-play-provider-evaluation.md
• Local code-review fallback: approved for docs-only change. No Unity, Nakama, package, scene, or provider-key changes.

Closes #249 only when implementation benchmark lands. This PR only seeds the design and backlog.