refactor: complete error handling standardization (issue #101)

Prestige Store:
- Convert doPrestige() to return Result<void> with specific error codes
  (INVALID_PRESTIGE_ID, PRESTIGE_MAX_LEVEL, INSUFFICIENT_INSIGHT)
- Convert startPactRitual() to return Result<void> with specific error codes
  (GUARDIAN_NOT_DEFEATED, PACT_ALREADY_SIGNED, PACT_SLOTS_FULL,
   INSUFFICIENT_MANA, RITUAL_IN_PROGRESS)

Combat Actions:
- Add try/catch wrapper inside processCombatTick with safe fallback defaults
- Add makeDefaultCombatTickResult helper for error recovery

LocalStorage Error Handling:
- Create safe-persist.ts utility wrapping localStorage with error handling
  (corrupted JSON, quota exceeded, unexpected failures)
- Update all 8 Zustand stores to use createSafeStorage() in persist middleware

UI Updates:
- Update GuardianPactsTab to use Result pattern for ritual error messages

Tests:
- Update store-actions-combat-prestige.test.ts for Result return types
- Update store-actions.test.ts ManaStore tests for Result pattern
- Remove duplicate Prestige/Discipline sections from store-actions.test.ts
- All files under 400 line limit

601 tests pass (3 pre-existing failures in spire-utils.test.ts)

src/lib/game/__tests__/store-actions-combat-prestige.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect, beforeEach } from 'vitest';
 import { useCombatStore } from '../stores/combatStore';
 import { usePrestigeStore } from '../stores/prestigeStore';
 import { getFloorMaxHP } from '../utils';
+import { ErrorCode } from '../utils/result';
 
 function resetCombatStore() {
   useCombatStore.setState({
@@ -188,7 +189,7 @@ describe('PrestigeStore', () => {
   describe('doPrestige', () => {
     it('should purchase upgrade when affordable', () => {
       const result = usePrestigeStore.getState().doPrestige('manaWell');
-      expect(result).toBe(true);
+      expect(result.success).toBe(true);
       expect(usePrestigeStore.getState().prestigeUpgrades.manaWell).toBe(1);
       expect(usePrestigeStore.getState().insight).toBeLessThan(500);
     });
@@ -196,18 +197,25 @@ describe('PrestigeStore', () => {
     it('should return false when cannot afford', () => {
       usePrestigeStore.setState({ insight: 0 });
       const result = usePrestigeStore.getState().doPrestige('manaWell');
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.INSUFFICIENT_INSIGHT);
+      }
     });
 
-    it('should return false for invalid upgrade id', () => {
+    it('should fail for invalid upgrade id', () => {
       const result = usePrestigeStore.getState().doPrestige('nonexistent');
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.INVALID_PRESTIGE_ID);
+      }
     });
 
     it('should increase memorySlots with deepMemory', () => {
       usePrestigeStore.setState({ insight: 2000 });
       const before = usePrestigeStore.getState().memorySlots;
-      usePrestigeStore.getState().doPrestige('deepMemory');
+      const deepResult = usePrestigeStore.getState().doPrestige('deepMemory');
+      expect(deepResult.success).toBe(true);
       expect(usePrestigeStore.getState().memorySlots).toBe(before + 1);
     });
   });
@@ -280,31 +288,43 @@ describe('PrestigeStore', () => {
     it('should start ritual when conditions met', () => {
       usePrestigeStore.setState({ defeatedGuardians: [10], signedPacts: [], insight: 10000 });
       const result = usePrestigeStore.getState().startPactRitual(10, 10000);
-      expect(result).toBe(true);
+      expect(result.success).toBe(true);
       expect(usePrestigeStore.getState().pactRitualFloor).toBe(10);
     });
 
     it('should return false when guardian not defeated', () => {
       const result = usePrestigeStore.getState().startPactRitual(10, 10000);
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.GUARDIAN_NOT_DEFEATED);
+      }
     });
 
-    it('should return false when already signed', () => {
+    it('should fail when already signed', () => {
       usePrestigeStore.setState({ defeatedGuardians: [10], signedPacts: [10] });
       const result = usePrestigeStore.getState().startPactRitual(10, 10000);
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.PACT_ALREADY_SIGNED);
+      }
     });
 
-    it('should return false when pact slots full', () => {
+    it('should fail when pact slots full', () => {
       usePrestigeStore.setState({ defeatedGuardians: [10], signedPacts: [20], pactSlots: 1 });
       const result = usePrestigeStore.getState().startPactRitual(10, 10000);
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.PACT_SLOTS_FULL);
+      }
     });
 
-    it('should return false when insufficient mana', () => {
+    it('should fail when insufficient mana', () => {
       usePrestigeStore.setState({ defeatedGuardians: [10], signedPacts: [] });
       const result = usePrestigeStore.getState().startPactRitual(10, 0);
-      expect(result).toBe(false);
+      expect(result.success).toBe(false);
+      if (!result.success) {
+        expect(result.code).toBe(ErrorCode.INSUFFICIENT_MANA);
+      }
     });
   });