perf(live): make Paper plugin scenario reproducible

[TypeThe0ry]

What changed

• Locks the compatible CraftEngine 26.7.4 artifact and updates checksums.
• Adds a Paper 1.20.1 command-map fallback for server-plugin descriptors that do not register commands.
• Lets the live runner stage and hash an exact MahjongPaper configuration fixture.
• Makes the bot-match state probe return the complete round summary.
• Documents deterministic terrain setup and expands runner/download tests.

Why

The previous live gate could fail before measurement because of an incompatible CraftEngine build, legacy Paper command registration, fresh-world placement restrictions, or an empty state summary. These were fixture failures rather than product regressions.

Impact

The fallback is used only when the modern lifecycle command API is unavailable and unregisters on shutdown. Public commands, gameplay configuration, persistence formats, and protocol behavior remain unchanged.

Validation

• TableViewerSnapshotFactoryOverheadTest
• 15 Python live-runner tests
• 3 Node protocol-frame tests
• shadowJar and spotlessCheck
• Paper 1.20.1 live smoke: scenario ready, TPS 20, 3,045 clientbound packets, graceful RCON shutdown

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