engine cleanup passes 4-7 + multi-instancing ambient rip

Squashes 146 commits from battle-engine-extraction. Net: 2,045 files changed,
+11,896 / -158,687 lines. Ships engine passes 4-7 (dead-code cull, view-layer
stub, receive-path shrink) plus the Phase-5 AsyncLocal ambient deletion that
turns concurrent battles into a type-system property rather than a scope
contract.

## What landed

**Passes 4-7 (chunks 1-34):** Extended the Phase-4 const-false collapse into a
cascading cull across the skill graph, view layer, and receive-path periphery.
Six mode flags (IsWatchBattle/IsReplayBattle/IsAdmin/IsAdminWatch/IsPuzzleQuest/
IsAINetwork) became `const false`, every guarded block deleted. Field*.cs
subclass ctors + BackGroundBase + ObjectChecker culled to no-ops. Mulligan
family reworked to take a mgr param through IMulliganMgr.InitMulligan.
Emotion/Recovery/Resource clusters null-stubbed. Prediction/OperationSimulator/
skill filters converted from static ambient reads to per-mgr reads via
SkillPrm.ownerCard.SelfBattlePlayer.BattleMgr / ins.BattleMgr / this.BattleMgr.

**Phase-5 ambient rip (chunks 35-47):** Deleted BattleAmbient / BattleAmbient-
Context / TestBattleScope in full. Every per-battle mutable slot now lives on
the mgr instance itself:
  mgr.InstanceIsForecast / InstanceIsRandomDraw / InstanceRecoveryInfo /
  InstanceViewerId / InstanceNetworkAgent / GameMgr
BattleManagerBase.GetIns() returns null unconditionally; the residual static
flags + 3 façades (Certification.ViewerId, Data.BattleRecoveryInfo,
ToolboxGame.RealTimeNetworkAgent) are null-tolerant defaults kept for the
handful of engine-internal readers that still reference their types. Zero
BattleAmbient references anywhere in engine + node + tests.

Added pre-seeded GameMgr ctor overload threaded through the mgr chain
(BattleManagerBase → SingleBattleMgr / NetworkBattleManagerBase → NetworkStandard-
BattleMgr → HeadlessBattleMgr / HeadlessNetworkBattleMgr). Fixtures build a
GameMgr, seed it via HeadlessEngineEnv.SeedCharaIds/SeedNetUser, and pass it
to the mgr's ctor — no ambient reach.

Node side (SVSim.BattleNode/SessionBattleEngine): _ctx replaced with a plain
GameMgr field; 34 `using var _ambient = BattleAmbient.Enter(_ctx)` scope wraps
ripped from every accessor and mutator; EngineGlobalInit.WirePerSessionGameMgr
takes GameMgr as a param and runs from SessionBattleEngine.SetupInternal
BEFORE mgr construction.

Test side: TestBattleScope deleted; 18 fixture [SetUp]s migrated to
`HeadlessEngineEnv.EnsureProcessGlobals()`; MultiInstanceEngineTests rewritten
around per-mgr construction (GetIns() → null is the pinned invariant).

## Regression fixes

- **chunk-48** (MulliganCtrl): chunk-35's `= null` stubs on card lookups broke
  the live receive-driven Deal path (BattlePlayerBase.DrawCard NRE'd downstream
  of NetworkPlayerMulliganCtrl.StartMulliganVfx). Restored the three lookups
  via `_battlePlayer.BattleMgr.GetBattleCardIdx`. Engine tests were satisfied
  by the WireMulliganPhase seam; unit tests exposed the live-path gap.

## Ship state

- SVSim.BattleEngine.Tests: 56/56 pass, 2 skip
- SVSim.UnitTests: 1554/1554 pass (was 1523/31-fail before chunk 48)
- Solution build: 0 source warnings (40 pre-existing NU1902 MessagePack CVEs
  in SVSim.EmulatedEntrypoint, unrelated)
- Sequential PVP smoke: verified live (two back-to-back battles, no regression
  on cleanup/spinup)
- Concurrent PVP smoke: verified live

Adds tools/engine-port/ClosureAnalyzer/ — the Roslyn transitive-type-closure
analyzer needed to make future cascade cleanup safe (per feedback memory
"Engine cleanup needs closure tool" from the 2026-06-28 pass-3 failure).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleEngine/Engine/AreaBGInfoSection20.cs

@@ -3,37 +3,6 @@ using Cute;
 
 public class AreaBGInfoSection20
 {
-	public const int SECTION_ID = 20;
-
-	public const int WERUSA_START = 10;
-
-	private const int WERUSA_END = 17;
-
-	private const int WERUSA_BG_SECTION_ID = 12;
-
-	private const int LEVIRU_START = 18;
-
-	private const int LEVIRU_END = 25;
-
-	private const int LEVIRU_BG_SECTION_ID = 10;
-
-	private const int IZUNIA_CHANGE_TEXTURE_START = 3;
-
-	private const int IZUNIA_END = 9;
-
-	private const int IZUNIA_BG_SECTION_ID = 2;
-
-	public const int NATERA_START = 26;
-
-	private const int NATERA_END = 33;
-
-	private const int NATERA_BG_SECTION_ID = 9;
-
-	private const int LAST_BATTLE_START = 34;
-
-	private const int LAST_BATTLE_END = 40;
-
-	private const int LAST_BATTLE_BG_SECTION_ID = 20;
 
 	public static List<ChapterExtraData> GetChapterExtraDatas()
 	{
@@ -62,7 +31,7 @@ public class AreaBGInfoSection20
 			if (i == 17 || i == 25 || i == 33)
 			{
 				chapterExtraData.BGExtraEffectPath = "scn_map_change_9";
-				chapterExtraData.SeType = Se.TYPE.SE_MAP_SECTION9_CHANGE_CHAPTER;
+				chapterExtraData.SeType = 0;
 			}
 			if (extraTextureIndex.IsNotNullOrEmpty())
 			{
@@ -83,7 +52,7 @@ public class AreaBGInfoSection20
 				SectionId = 20,
 				ExtraTextureChapter = 1,
 				BGExtraEffectPath = "scn_map_change_9",
-				SeType = Se.TYPE.SE_MAP_SECTION20_CHANGE_CHAPTER1
+				SeType = 0
 			},
 			new ChapterExtraData
 			{
@@ -91,7 +60,7 @@ public class AreaBGInfoSection20
 				ExtraTextureChapter = 2,
 				BGExtraEffectPath = "scn_map_change_8",
 				AttachExtraEffectToBgRoot = true,
-				SeType = Se.TYPE.SE_MAP_TREE_EFFECT
+				SeType = 0
 			}
 		};
 	}
@@ -112,7 +81,7 @@ public class AreaBGInfoSection20
 			if (i == 9)
 			{
 				chapterExtraData.BGExtraEffectPath = "scn_map_change_9";
-				chapterExtraData.SeType = Se.TYPE.SE_MAP_SECTION9_CHANGE_CHAPTER;
+				chapterExtraData.SeType = 0;
 			}
 			list.Add(chapterExtraData);
 		}