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.Tests/NetworkEmitFixtureBase.cs

@@ -3,16 +3,17 @@ namespace SVSim.BattleEngine.Tests
     // Shared base for every network-emit test fixture (M13 EmitPathReadOracleTests, the
     // construction-probe's OnEmit seam test, and any M14+ network fixture to come).
     //
-    // POST-TASK-8 (multi-instancing migration): now empty. The historical hygiene gap this class
-    // closed (HeadlessEngineEnv.NewNetworkEmitBattle leaving IsForecast=false + a stray injected
-    // agent visible to a later solo fixture) was a PROCESS-GLOBAL leak via the now-deleted
+    // Post-Phase-5a: still empty. The historical hygiene gap this class closed
+    // (HeadlessEngineEnv.NewNetworkEmitBattle leaving IsForecast=false + a stray injected agent
+    // visible to a later solo fixture) was a PROCESS-GLOBAL leak via the long-deleted
     // BattleManagerBase._isForecastFallback + ToolboxGame._realTimeNetworkAgentFallback statics.
-    // Both fields are gone: IsForecast/RealTimeNetworkAgent live on the per-test ambient context
-    // (TestBattleScope's BattleAmbientContext), so scope Dispose drops them. A later fixture's
-    // new TestBattleScope starts a fresh ctx with IsForecast=true and a null NetworkAgent by
-    // default — exactly the EnsureInitialized invariant the old TearDown manually restored.
+    // As of Phase 5a IsForecast/RealTimeNetworkAgent live on the mgr instance (authoritative)
+    // with the per-test BattleAmbientContext as bridge fallback: scope Dispose drops the ctx and
+    // the next fixture's new TestBattleScope starts a fresh ctx with IsForecast=true and a null
+    // NetworkAgent — exactly the EnsureInitialized invariant the old TearDown restored.
     //
-    // Kept as a marker base class so derived fixtures don't churn; can be deleted in Task 9.
+    // Kept as a marker base class so derived fixtures don't churn; deleteable once every
+    // fixture stops touching the ambient (Phase 5b + ambient rip).
     public abstract class NetworkEmitFixtureBase
     {
     }