[NutyoPR]

Plugin API: expose the party leader

Adds SkyrimTogetherGetPartyLeaderId, an optional export next to SkyrimTogetherRegisterScopedChannel, returning the party leader's player ID (0 while not in a party).

Why: the party leader hosts the world's NPCs and quest scenes, so plugins that move NPCs or start scenes need to do it on the leader's client only. Today a plugin can only approximate that (e.g. "lowest player ID"), which picks the wrong client whenever the leader isn't the lowest ID, and changes after a reconnect. Enderal AllTogether https://github.com/NutyoPR/EnderalAllTogether needs this for patched quest scenes that otherwise move the same NPC on both clients and leave it frozen.

How: same pattern as scoped channels, nothing in the V1 vtable changes.

• SkyrimTogetherAPI.h: GetPartyLeaderId_t and kGetPartyLeaderIdName, documented.
• PluginAPI.cpp: the export.
• PluginService: caches PartyService::GetLeaderPlayerId() in the existing per-update snapshot (under m_lock, like m_inParty), so it's callable from any thread.
• plugin_api/README.md: a short "Party leader" section with a lookup example and fallback.

Older executables simply don't have the symbol, so plugins fall back gracefully. No protocol change.

Tested: not yet in game; needs a build and a two-client check that both clients report the same leader ID and that it follows a leadership change.

[NutyoPR]

tested in game with 2 clients on 1.7.104: both clients find the export and report the same leader id, and it stays correct when the other player reconnects with a new id. haven’t tested handing leadership over yet, will update if i do