Complete early roadmap foundation and calendar helpers

Docs/GameplayAbilitySystemDecision.md

@@ -0,0 +1,37 @@
+# Gameplay Ability System Decision
+
+Decision: defer Unreal's Gameplay Ability System for the MVP.
+
+Agrarian should not adopt GAS during version 0.01 or the early version 0.1
+survival foundation. The current project already has focused replicated
+components for survival, inventory, crafting, resources, building placement,
+time, weather, interaction, and early movement modifiers. Those systems are
+small, readable, and directly aligned with the immediate playable MVP.
+
+GAS is useful for games with many networked abilities, buffs, cooldowns,
+attribute effects, prediction needs, tags, and reusable gameplay effects. That
+will probably matter later for Agrarian when character skills, injuries,
+illnesses, professions, equipment, medicine, combat, aging, and long-term
+condition effects become more complex.
+
+For now, adding GAS would increase setup cost, content complexity, debugging
+surface, and onboarding burden before the project has enough gameplay variety
+to benefit from it.
+
+Guideline:
+
+- Keep MVP survival systems implemented through explicit C++ components and
+  Blueprint assets.
+- Keep future stat/effect code modular enough that it can migrate into GAS if
+  the need becomes clear.
+- Revisit GAS after version 0.1 once combat, skills, injuries, medicine,
+  profession bonuses, equipment effects, and replicated long-term status
+  modifiers are better defined.
+
+Revisit trigger:
+
+- The project has many recurring timed effects, buffs, debuffs, cooldowns, or
+  ability activations that are becoming duplicated across systems.
+- Multiplayer prediction for ability-style actions becomes important.
+- Designers need data-driven effect stacking, gameplay tags, and reusable
+  effect authoring more than hand-coded component behavior.