fix(config): use SnakeYAML default ctor (2.x compatible) for existing-config load

[minekube-ai-engineer]

Source: Discord ask-support thread

Root cause: 0.15.10 (PR #157, commit 4932eb4) added new Yaml(new SafeConstructor()) in ConfigLoader.hasBedrockIdentitySection. SnakeYAML 2.0 removed the no-arg SafeConstructor constructor, and Velocity 4.x supplies SnakeYAML 2.x at runtime (through Configurate) — the velocity module declares snakeyaml as provided, so the plugin jar does not bundle it. Every existing-config.yml load on Velocity therefore crashed with NoSuchMethodError: org.yaml.snakeyaml.constructor.SafeConstructor: method 'void <init>()' not found, wrapped in the misleading RuntimeException: Failed to load the config! Try to delete the config file.... Deleting config.yml does not help — the crash only fires when a config.yml exists. Spigot/Bungee platforms (SnakeYAML 1.x) were unaffected; 0.15.9 and earlier had no such code path.

Fix: construct new Yaml() — the default constructor delegates to SafeConstructor internally in both SnakeYAML 1.x and 2.x. No project-wide 2.x API bump is needed: a repo-wide grep shows this was the only production new SafeConstructor() / non-default new Yaml(...) usage (the other new Yaml( call sites are release-verification tests already on the default ctor, which is safe on both APIs).

Regression coverage (TDD RED → GREEN):

• core/build.gradle.kts: core test classpath now pins SnakeYAML 2.2 (the major version Velocity actually provides at runtime), so the config-loading tests exercise the platform API instead of the compile-time 1.28.
• New test ConfigLoaderTest.legacyConfigLoadsOnSnakeYaml2xRuntimeClasspath fails on the unfixed code with the exact production signature — Caused by: java.lang.NoSuchMethodError: org.yaml.snakeyaml.constructor.SafeConstructor: method 'void <init>()' not found at ConfigLoader.java:74 — and passes on the fix.
• Full :core:test suite: 67 classes / 347 tests / 0 failures / 0 errors (all 8 ConfigLoaderTest cases green on the 2.x classpath).