Herblore rework: tiered potion ladders per skill

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -44,11 +44,14 @@ Alpha. One season, bandit raids plus two friendly events, six buildings.
   fight while their points last, and praying trains Prayer too. A Temple adds
   points per bone and lets players offer bones as devotion, which wards the
   city in the next raid.
-- **Herblore:** farmers grow six herbs (guam to snapdragon); herblore brews
-  them with a secondary into potions of 50 uses. One potion per skill at a
-  time: faster gathering, a chance to keep materials or double ore, more
-  prayer from bones, or combat power, armour and healing. An empty potion is
-  replaced from the bank automatically.
+- **Herblore:** farmers grow six herbs (guam to snapdragon), one per tier.
+  Every potion is a ladder of up to six tiers (I–VI): the tier's herb plus
+  the matching rung of the skill's own resources (copper ore → runite ore,
+  logs → enchanted logs, copper bar → rune bar…), at Herblore 1, 15, 30, 45,
+  60 and 75. Gathering and Construction potions are 10–35% faster, crafting
+  potions a 10–35% chance to keep materials, Prayer more points from bones,
+  and combat has Strength and Defence ladders. Potions last 50 uses, one per
+  skill at a time; an empty one is replaced from the bank automatically.
 - **Events:** raids are announced a day or two ahead. Reconnaissance from
   scouts, informants and the spymaster's guild narrows down when, how strong,
   and finally where their camp is, so fighters can sabotage it. Fighters can