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/effects/upgrade-effects.ts

@@ -18,10 +18,7 @@ function _buildUpgradeCache(): void {
  * Get all selected upgrades with their full effect definitions.
  * Since skills are removed, always returns empty array.
  */
-export function getActiveUpgrades(
-  _skillUpgrades: Record<string, string[]>,
-  _skillTiers: Record<string, number>
-): ActiveUpgradeEffect[] {
+export function getActiveUpgrades(): ActiveUpgradeEffect[] {
   return [];
 }
 
@@ -29,10 +26,7 @@ export function getActiveUpgrades(
  * Compute all active effects from selected upgrades.
  * Since skills are removed, returns base values with no upgrades applied.
  */
-export function computeEffects(
-  _skillUpgrades: Record<string, string[]>,
-  _skillTiers: Record<string, number>
-): ComputedEffects {
+export function computeEffects(): ComputedEffects {
   return {
     maxManaMultiplier: 1,
     maxManaBonus: 0,