Add GiveItems command for member-to-member handoffs

[mmacy]

Summary

Adds GiveItems, a command that hands items and coins from one party member to another in zero game time — the distribute-the-load move for shifting weight off an overloaded companion so the party's marching rate recovers.

• Legal in town and while exploring (not mid-encounter or in battle); both members must be able-bodied and distinct.
• A given magic item releases its worn effects and lands unequipped in the recipient's pack; mundane items merge into a like stack; valuables and coins move across.
• Emits a player-visible ItemsGivenEvent.
• The giver must actually carry what's named, and a revealed cursed item cannot be handed off.

Implementation notes

• The carried-goods check shared by drop and give is factored out of DropItems into a renamed _validate_carried(member, item_ids, coins) guard, and _handle_drop_during_encounter updated to match.
• New exploration.give.same_member rejection (documented in rejection_codes.json), plus the exploration.item.given message template.

Testing

• Full suite: 1556 passed, 58 skipped.
• New TestGiveItems covers coins + mundane item transfer, valuables, zero-time, relieving an overloaded/frozen party, and rejections (lacks item, insufficient coin, self-gift, unknown recipient, allowed in town).
• Docs-gate tests confirm the new rejection code and event stay in sync with the generated reference.

Left in [Unreleased] in the changelog — no release cut for this.

https://claude.ai/code/session_015gLzwFqWygcffUqqhwb9Zh