Integrate geysermc and floodgate for bedrock support

[robinbraemer]

Add a built-in Floodgate trust plugin to Gate to allow authenticated Bedrock players to bypass Mojang authentication.

This feature enables Gate to trust upstream Geyser/Floodgate proxies, which handle Bedrock protocol translation and authentication. By detecting Floodgate-specific handshake data and/or trusted source IPs, Gate can force offline mode for these connections, preventing redundant Mojang authentication for Bedrock players.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[robinbraemer]

Closing as superseded.

This draft predates the current Connect-managed Bedrock direction and the shipped identity rollout. The replacement work is now tracked/landed through:

• minekube/moxy#429: Bedrock identity metadata/envelope rollout
• Load Bedrock identity verifier metadata connect-java#53 + release 0.10.0: verifier metadata and endpoint/org-scoped enforcement
• Document Bedrock identity rollout #123: Bedrock identity docs
• production verification: https://github.com/minekube/moxy/actions/runs/28841511840

The remaining follow-up direction should be tracked as product/issues rather than reviving this old built-in Floodgate/Geyser draft.