Support Floodgate (Bedrock) left-click selling and add build artifact workflow

[iphonetips1]

Motivation

• Allow Bedrock players (via Floodgate/Floodgate API) to use left-click to trigger a sell to match platform UX differences while preserving cooldown behavior.
• Add a CI workflow to produce and upload a plugin jar artifact on pull requests and manual runs.

Description

• Treat left-clicks as valid sell attempts when the interacting player is a Bedrock/Floodgate player by introducing a shouldSell condition and using it for sell logic and cooldown checks.
• Added isBedrockPlayer(Player) which uses reflection to call org.geysermc.floodgate.api.FloodgateApi#getInstance and isFloodgatePlayer(UUID) so the plugin does not hard-depend on Floodgate at compile time and safely falls back if the API is absent or inaccessible.
• Updated logic so cooldown enforcement uses the new shouldSell boolean and consolidated the sell handling branch to use it instead of only Action.RIGHT_CLICK_BLOCK.
• Added a GitHub Actions workflow .github/workflows/build-artifact.yml that sets up Java (Temurin 21), caches Maven, runs mvn -B -DskipTests package, and uploads target/*.jar (excluding original-*.jar) as the AxSellwands-jar artifact on pull requests or manual dispatches.

Testing

• No automated unit tests were executed by this change because the workflow is configured to run mvn -DskipTests package which explicitly skips test execution.
• A CI packaging job was added to build and upload the jar artifact via the new GitHub Actions workflow and will run on pull requests or manual workflow_dispatch events.

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Codex Task