Rank remaining unified bytecode gaps

[rogeralsing]

Summary

• make the ranked unsupported-bucket list cover activation-model gaps, not only expression/call neighbors
• clarify that property and assignment work is now narrower but still has private, optional, dynamic, richer computed-key, and computed compound/logical/update gaps
• keep resumable unified bytecode called out as narrower than ordinary sync production bytecode

Verification

• rtk git diff --check
• rtk rg -n "Activation model gaps|Property and assignment widening|EvaluateResumable|computed expression-key compound" docs/unified-bytecode-expansion-contract.md
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums" (1 passed; 7 unrelated existing nullable warnings in test files)

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