[49] [C#-QUEST.2/3] Quest accept/complete/reward side-effects incomplete

[alseif0x]

• QUEST.2: HandleQuestgiverAcceptQuest misses item/player sharing, close-gossip, CanAddQuest, source item/spell, scripts, quest tracker, push-to-party, launch gossip.
• QUEST.3: complete/request-items/choose-reward runtime is partial (empty request-items, incomplete CanRewardQuest, RewardQuest gates/side-effects).
  C++: Handlers/QuestHandler.cpp; Entities/Player/Player.cpp (AddQuest/RewardQuest). Complements M4.7 ([43] [M4.7] Quest objective auto-credit (kill/loot/explore) + apply rewards live #41).

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From the C#-vs-C++ reference audit (local docs/audits/csharp-reference-contrast.md). Plan: docs/migration/PORT_PLAN.md (L26) · State: docs/migration/STATE.md.
Done = contrast Rust vs the cited C++; if it matches, re-anchor the comment to C++ file:line; if it differs, fix behavior to C++. Live + capture-clean. 1 issue = 1 PR.