Moves the two quest-reward mutation handlers
(--add-quest-reward-item, --set-quest-reward) out of main.cpp
into a new cli_quest_reward.{hpp,cpp} module. Both operate on
a quest's reward struct in zone.json: the first greedy-consumes
multiple item paths in one invocation, the second uses
order-independent flag/value pairs (--xp / --gold / --silver
/ --copper) with strict 'only changed fields are written'
semantics so partial updates don't clobber unrelated fields.
main.cpp shrinks by 114 lines (6,429 to 6,315).
