feat(config): add validated durable Leaf state

src/main/resources/config.yml

@@ -0,0 +1,15 @@
+# Whether Leaf protection is available server-wide.
+enabled: true
+
+# Visible Minecraft Resistance level (I-V).
+resistance-level: 1
+
+# Legacy color codes are supported.
+prefix: "&a🍃 "
+
+# Calendar-day onboarding window measured from first join.
+onboarding-days: 7
+
+welcome-message: "&aLeaf protection is available: /leaf on, /leaf off, or /leaf status. Attacking another player opts you out."
+combat-disabled-message: "&cLeaf protection was disabled because you attacked another player."
+locked-message: "&cAn administrator locked your Leaf setting."