Fix research sync toggle and classic medikit crash

[xcomcoopdev]

Summary

This fixes two co-op issues:

1. Setting Enable Research Sync (Separate) to NO did not disable research synchronization because the actual send, receive, and apply paths ignored the negotiated value.
2. Healing performed by a client in classic-turn co-op could crash the host because the replayed action did not contain a medikit weapon.

It also prevents a disabled PvP reaction-fire setting from leaking into later non-PvP co-op sessions.

Disabled research synchronization

• Do not send research completions when Enable Research Sync (Separate) is set to NO.
• Ignore incoming research packets while synchronization is disabled.
• Do not apply or retain queued research while synchronization is disabled.
• Mirror the host-authoritative value to the client's Multiplayer options UI.
• Prevent the client from overriding the host's value while connected.
• Propagate host changes to the client during an active session.
• Rename the displayed option to Enable Research Sync (Separate).
• Fix the research packet typo from base_lot to base_lon.

Classic medikit crash

The classic replay path reused the host's current BattleAction. It assigned the actor, action type, and TU cost, but never assigned action->weapon.

TileEngine::medikitUse() subsequently dereferenced:

action->weapon->getRules()

This caused an access violation when a client healed a soldier and the host's current action had no weapon.

The fix:

• Uses a stack-local replay action in both classic and parallel turns.
• Resolves the healer's actual medikit using the packet's healer, weapon, type, and hand identifiers.
• Validates the healer, medikit type, and body part.
• Safely skips malformed or stale packets.
• Adds a defensive null check to TileEngine::medikitUse().

PvP reaction fire

• Reset the session reaction-fire value to enabled in non-PvP modes.
• This prevents Enable Reaction Fire in PvP = NO from affecting a later normal co-op campaign.

Testing

• Reproduced the classic-turn crash with a client healing a soldier.
• Confirmed the crash occurred at action->weapon->getRules() with a null weapon.
• Manually verified after the fix that client healing succeeds and the host no longer crashes.