feat: route simple optional computed delete

[rogeralsing]

Summary

• admit delete box?.[key] into production unified bytecode via the existing optional computed delete short-circuit lowering
• keep optional named delete and chained optional delete neighbors as explicit declines
• add public route proof and update the unified-bytecode contract/rule docs

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedName~UnifiedBytecodeProductionEligibilityTests.Evaluate_OptionalComputedPropertyDeleteCandidate_AcceptsOwnedPropertyOpcodes|FullyQualifiedName~UnifiedBytecodeProductionEligibilityTests.Evaluate_OptionalPropertyDelete_DeclinesWithExplicitCode|FullyQualifiedName~UnifiedBytecodeProductionEligibilityTests.Evaluate_UnsupportedOptionalComputedPropertyDeleteNeighbor_DeclinesWithExplicitCode|FullyQualifiedName~UnifiedBytecodeProductionInvocationTests.SimpleOptionalComputedPropertyDelete_UsesUnifiedBytecodeProductionFastPathAndSkipsNullishKey|FullyQualifiedName~UnifiedBytecodeProductionInvocationTests.OptionalComputedPropertyDelete_UsesUnifiedBytecodeProductionFastPathAndSkipsNullishKey"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedName~UnifiedBytecodeProductionEligibilityTests|FullyQualifiedName~UnifiedBytecodeProductionInvocationTests|FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums"
• rtk rg "EvaluateExpression\\(|ProfileEvaluateExpression\\(" src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner* (no matches)
• rtk ./tools/profile forloop --memory (Total allocated 6.85 MB)
• rtk git diff --check

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