Redesign skill system with upgrade trees and tier progression

Major changes:
- Created docs/skills.md with comprehensive skill system documentation
- Rewrote skill-evolution.ts with new upgrade tree structure:
  - Upgrades organized in branching paths with prerequisites
  - Each choice can lead to upgraded versions at future milestones
  - Support for upgrade children and requirement chains
- Added getBaseSkillId and generateTierSkillDef helper functions
- Fixed getFloorElement to use FLOOR_ELEM_CYCLE.length
- Updated test files to match current skill definitions
- Removed tests for non-existent skills

Skill system now supports:
- Levels 1-10 for most skills, level 5 caps for specialized, level 1 for research
- Tier up system: Tier N Level 1 = Tier N-1 Level 10 in power
- Milestone upgrades at levels 5 and 10 with branching upgrade trees
- Attunement requirements for skill access and tier up
- Study costs and time for leveling

src/lib/game/stores/uiStore.ts

@@ -0,0 +1,74 @@
+// ─── UI Store ────────────────────────────────────────────────────────────────
+// Handles logs, pause state, and UI-specific state
+
+import { create } from 'zustand';
+
+export interface LogEntry {
+  message: string;
+  timestamp: number;
+}
+
+export interface UIState {
+  logs: string[];
+  paused: boolean;
+  gameOver: boolean;
+  victory: boolean;
+  
+  // Actions
+  addLog: (message: string) => void;
+  clearLogs: () => void;
+  togglePause: () => void;
+  setPaused: (paused: boolean) => void;
+  setGameOver: (gameOver: boolean, victory?: boolean) => void;
+  reset: () => void;
+  resetUI: () => void;
+}
+
+const MAX_LOGS = 50;
+
+export const useUIStore = create<UIState>((set) => ({
+  logs: ['✨ The loop begins. You start with Mana Bolt. Gather your strength, mage.'],
+  paused: false,
+  gameOver: false,
+  victory: false,
+  
+  addLog: (message: string) => {
+    set((state) => ({
+      logs: [message, ...state.logs.slice(0, MAX_LOGS - 1)],
+    }));
+  },
+  
+  clearLogs: () => {
+    set({ logs: [] });
+  },
+  
+  togglePause: () => {
+    set((state) => ({ paused: !state.paused }));
+  },
+  
+  setPaused: (paused: boolean) => {
+    set({ paused });
+  },
+  
+  setGameOver: (gameOver: boolean, victory: boolean = false) => {
+    set({ gameOver, victory });
+  },
+  
+  reset: () => {
+    set({
+      logs: ['✨ The loop begins. You start with Mana Bolt. Gather your strength, mage.'],
+      paused: false,
+      gameOver: false,
+      victory: false,
+    });
+  },
+
+  resetUI: () => {
+    set({
+      logs: ['✨ The loop begins. You start with Mana Bolt. Gather your strength, mage.'],
+      paused: false,
+      gameOver: false,
+      victory: false,
+    });
+  },
+}));