…er, HTMLCache) + refined blockers for the remaining 4

PeriodicInstanceManager (beyond-aion#3) + HTMLCache (beyond-aion#4) wired via real-data fixture seeds. The
other 4 sit at a real floor: beyond-aion#1 SiegeService.initSieges + beyond-aion#5 PvpMapService need the heavy
SPAWNS_DATA + world-map boot (beyond-aion#5 also breaks the empty-world invariant); beyond-aion#2 Housing is
DB-required with no Java null guard; #6 PeriodicSaveService is a coordinated DI->singleton
re-port. Documented precise blockers + recommended harnesses.

… spawn-backed harness for beyond-aion#1/beyond-aion#5

#6 PeriodicSaveService re-ported faithful 1:1 (commit 62c4083). Added a full read-only
scope for the spawn-data-backed bootstrap harness that unblocks beyond-aion#1 SiegeService.initSieges +
beyond-aion#5 PvpMapService together: substrate (SPAWNS_DATA/WORLD_MAPS_DATA loaders + SpawnEngine.SpawnAll)
already done, work is fixture data-seeding (real spawns/ + world_maps.xml + NPC_DATA via the
existing CopyRealFile mechanism) + flipping 2 wires + reworking the empty-world assert. Effort
MEDIUM, recommend a NEW spawn-backed bootstrap test to preserve the minimal-fixture invariants.

…3 spawn-path faithfulness bugs

New GameServerBootstrapTests.GameServerBootstrap_RealSpawnDataMaterializesNpcsIntoWorld: loads the REAL
game-server data+cache (DataManager.LoadAsync(repoRoot)), brings up the real boot machinery (DataManager +
World maps + IDFactory/ThreadPool bridges + AIEngine/ZoneService/GeoService), drives the faithful
SpawnEngine.SpawnObject path over Sanctum's real SPAWNS_DATA, and asserts the World store materializes real
Npc instances (357 NPCs incl. Euterpe 798173). End-to-end proof that the SPAWNS_DATA fix spawns NPCs (was 0).

Three faithfulness fixes the spawn path surfaced:
- GameServerBootstrapService: move engine-init to its Java-correct order (parallel, after DataManager, before
  the location-init/spawn services) - AIEngine must be up before any Npc spawn resolves its AI.
- GameServerBootstrapService: bind IDFactory.RegisterInstance(_idFactory) after LockIds (every VisibleObject
  ctor reads IDFactory.GetInstance().NextId(); was a latent production boot NRE).
- AIName: [AttributeUsage(Inherited=false)] to match Java's non-@inherited @ainame (SiegeNpcAI extends
  AggressiveNpcAI must NOT inherit "aggressive" -> was double-registering). Plus a defensive TypeLoad guard in
  OnClassLoadUnloadListener.DoMethodInvoke for the C# whole-AppDomain script scan (production unaffected).

Siege/PvP wires (beyond-aion#1/beyond-aion#5) stay deferred in StartAsync: confirmed via Java source neither guards empty data
(siege updateFortressNextState NREs on null getSiegeLocation; pvp init needs world map 301220000), so they
cannot be unconditionally on under the minimal-fixture bootstrap. Full SpawnAll boot also needs a DB (beyond-aion#2
HousingService). Findings + recommended next documented in docs/next-slop-targets.md.

Per-class GREEN: build 0, Bootstrap 8/8, Golden 167/167, RealStaticDataLoad 1/1.