Added

• Acrobatics skill — tracks XP earned from jumping, falling, and sprinting (ACROBATICS enum constant, Feather GUI icon, xp-base: 80.0, xp-multiplier: 1.4, max-level: 100)
• Custom skills API — third-party plugins can now register their own skills at runtime via SkillDefinition and EzSkillsAPI.registerSkill(); progress is persisted in the same storage backend as built-in skills
• SkillDefinitionRegistry — thread-safe in-memory registry for custom SkillDefinition instances; rejects names that clash with built-in SkillType values
• EzSkillsAPI.getRegisteredSkills() — returns the list of all currently registered custom skill definitions
• Custom skill XP / level methods on EzSkillsAPI: addExperience, getSkillLevel, getSkillExperience, setSkillLevel now accept any registered custom skill name in addition to built-in SkillType names

Changed

• Skill GUI (/skills) updated to a 36-slot (4-row) layout to accommodate five built-in skills; close button moved to slot 31
• SkillProfile stores custom skill progress in a separate HashMap alongside the built-in EnumMap; getAllCustom() exposes the full map for serialisation
• SkillProfileModel persists and loads custom skill columns (<name>_level / <name>_experience) automatically

Skills

Skill	Enum	XP base	XP multiplier	Max level
Woodcutting	WOODCUTTING	100.0	1.5	100
Mining	MINING	100.0	1.5	100
Fishing	FISHING	100.0	1.5	100
Fighting	FIGHTING	120.0	1.6	100
Acrobatics	ACROBATICS	80.0	1.4	100

Abilities

Ability	Skill	Trigger
Lumberjack	Woodcutting	Auto-smelt logs on break
Spelunker	Mining	Night-vision while underground
Angler	Fishing	Reduced fishing wait time
Warrior	Fighting	Temporary strength boost on kill streak