🐛 `GetNPCByID` and `GetMobByID` emit spurious warnings for content-disabled entities

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Summary

When RESTRICT_CONTENT = 1 and one or more ENABLE_* flags are set to 0 in
settings/main.lua, any NPC or mob whose content_tag matches a disabled
expansion is intentionally skipped during LoadNPCList / LoadMOBList. However,
scripts that call GetNPCByID or GetMobByID on those IDs still trigger a
ShowWarning log entry, even though the absence of the entity is expected
behavior.

This floods the server log with false-positive warnings, making it harder to
spot genuine issues.

Reproduction steps

1. Set RESTRICT_CONTENT = 1 in settings/main.lua.
2. Set any expansion flag to 0, e.g. ENABLE_COP = 0.
3. Start the map server.
4. Observe repeated luautils::GetNPCByID NPC doesn't exist (XXXXXXXX) and
   luautils::GetMobByID Mob doesn't exist (XXXXXXXX) warnings in the log for
   NPCs / mobs whose content_tag is COP.

Expected behavior

No warning should be emitted when GetNPCByID / GetMobByID is called for an
entity that was intentionally excluded from loading due to its content_tag.

Proposed fix

After LoadNPCList and LoadMOBList complete, build an in-memory set of
disabled entity IDs by querying npc_list and mob_spawn_points JOIN mob_groups
for rows whose content_tag maps to a disabled ENABLE_* key. Then, in
GetNPCByID / GetMobByID, skip ShowWarning when the requested ID is found
in that set.

// zoneutils.h
extern std::unordered_set<uint32> disabledContentNpcIds;
extern std::unordered_set<uint32> disabledContentMobIds;
void BuildDisabledContentSets();

// zoneutils.cpp — called once after LoadNPCList + LoadMOBList
void BuildDisabledContentSets() {
    auto rsetNpc = db::preparedStmt(
        "SELECT npcid, content_tag FROM npc_list WHERE content_tag IS NOT NULL");
    while (rsetNpc->next()) {
        if (!luautils::IsContentEnabled(rsetNpc->get<std::string>("content_tag")))
            disabledContentNpcIds.insert(rsetNpc->get<uint32>("npcid"));
    }
    auto rsetMob = db::preparedStmt(
        "SELECT mob_spawn_points.mobid, mob_groups.content_tag "
        "FROM mob_spawn_points "
        "INNER JOIN mob_groups ON mob_spawn_points.groupid = mob_groups.groupid "
        "WHERE mob_groups.content_tag IS NOT NULL");
    while (rsetMob->next()) {
        if (!luautils::IsContentEnabled(rsetMob->get<std::string>("content_tag")))
            disabledContentMobIds.insert(rsetMob->get<uint32>("mobid"));
    }
}

// luautils.cpp — GetNPCByID
if (!PNpc) {
    if (zoneutils::disabledContentNpcIds.find(npcid) ==
        zoneutils::disabledContentNpcIds.end())
        ShowWarning("luautils::GetNPCByID NPC doesn't exist (%d)", npcid);
    return nullptr;
}

Environment

• OS: Windows 11
• Branch: base