feat(csharp): add inventory menus

[RestartFU]

What

• add a native C# Inv API for chest, double-chest, hopper, dropper, barrel, and ender-chest menus
• bridge typed item stacks plus repeatable submit and terminal close callbacks across ABI v69
• implement fake-container session state, packet normalization, safe replacement/rollback, disconnect, and runtime-drain cleanup
• add the /kitchen inv example, documentation, and lifecycle/race coverage

Why

C# plugins can currently show forms, but cannot present interactive Bedrock inventory menus. This adds the inventory-menu behavior directly to the plugin runtime and host without requiring a Dragonfly fork.

Impact

• bumps the host ABI from 68 to 69, so the runtime and host must be upgraded together
• uses the pinned Dragonfly session layout and fails fast if its private fields change
• preserves real-container state, temporary UI items, fake block restoration, callback ownership, and host isolation

Checks

• make test
• go test -race ./internal/host ./internal/native ./framework
• dotnet build csharp/Dragonfly/Dragonfly.csproj -c Release --no-restore
• branch autoreview; all actionable findings addressed