refactor: remove skill system leftovers, migrate click mana to discipline perk

- Simplified getMeditationBonus() to continuous ramp formula
- Added click-mana capped perk to Mana Circulation discipline
- Removed manaWell/manaFlow/manaSpring skill reads and prestige upgrades
- Removed all skill fields from GameState and GameActionType
- Updated all call sites and tests (916 tests passing)

Closes #174

src/lib/game/data/disciplines/base.ts

@@ -61,10 +61,19 @@ export const baseDisciplines: DisciplineDefinition[] = [
         type: 'capped',
         threshold: 100,
         value: 100,
-        description: 'Every 100 XP: +0.5 max meditation cap (7 tiers, up to +3.5). Raises Void Meditation ceiling.',
+        description: 'Every 100 XP: +0.5 to meditation multiplier (7 tiers, up to +3.5). Adds directly to the meditation multiplier cap.',
         bonus: { stat: 'meditationCapBonus', amount: 0.5 },
         maxTier: 7,
       },
+      {
+        id: 'mana-circulation-click',
+        type: 'capped',
+        threshold: 500,
+        value: 500,
+        description: 'Every 500 XP: +1 mana per click (5 tiers, up to +5).',
+        bonus: { stat: 'clickManaBonus', amount: 1 },
+        maxTier: 5,
+      },
     ],
   },
   {