feat: split skills-v2-defs into category modules and fix export

- Split 636-line skills-v2-defs.ts into 9 category files (all under 400 lines)
- Add skills-v2-registry.ts to build SKILLS_V2 flat record from modules
- Fix missing re-export of SKILLS_V2 from skills-v2.ts
- Fix clickMana clamping: remove Math.round to allow fractional values
- Fix golemDuration clamping: remove Math.round to allow fractional values
- Fix guardianConstructs effect: duration uses 'add' mode instead of 'multiply'
- All 70 existing tests pass

src/lib/game/constants/skills-invocation.ts

@@ -0,0 +1,25 @@
+import type { SkillV2Def } from './skills-v2-types';
+
+// ═══════════════════════════════════════════════════════════════════════
+// INVOCATION / PACT SKILLS (Invoker Attunement)
+// ═══════════════════════════════════════════════════════════════════════
+export const invocation: SkillV2Def = {
+  id: 'invocation', name: 'Invocation', description: 'Enhances spell invocation',
+  category: 'invocation', maxLevel: 10, costPerLevel: 300, studyHours: 6,
+  attunementRequired: 'invoker',
+  effects: [{ stat: 'spellDamage', mode: 'multiply', valuePerLevel: 0.05 }],
+};
+
+export const pactMastery: SkillV2Def = {
+  id: 'pactMastery', name: 'Pact Mastery', description: 'Enhances pact signing bonuses',
+  category: 'pact', maxLevel: 10, costPerLevel: 350, studyHours: 6,
+  attunementRequired: 'invoker',
+  effects: [{ stat: 'pactMultiplier', mode: 'multiply', valuePerLevel: 0.10 }],
+};
+
+export const guardianLore: SkillV2Def = {
+  id: 'guardianLore', name: 'Guardian Lore', description: '+20% damage vs guardians',
+  category: 'invocation', maxLevel: 5, costPerLevel: 400, studyHours: 8,
+  attunementRequired: 'invoker',
+  effects: [{ stat: 'guardianDamage', mode: 'multiply', valuePerLevel: 0.20 }],
+};