Update documentation after refactoring: AGENTS.md, GAME_BRIEFING.md, skills.md

- Updated AGENTS.md to include store/ directory and clarify store architecture
- Updated GAME_BRIEFING.md Code Architecture section with store/ and legacy store info
- Updated skills.md with skill state management information
- Includes other refactoring changes (store hooks, component updates, etc.)

docs/GAME_BRIEFING.md

@@ -1083,7 +1083,9 @@ dps = (damage × castSpeed × attackSpeedMultiplier) / hour
 
 The codebase has been refactored into a modular architecture for better maintainability:
 
-#### Store Architecture (`src/lib/game/stores/`)
+#### Store Architecture
+
+**New Modular Stores (`src/lib/game/stores/`):**
 - **gameStore.ts**: Core state, tick logic, and main actions
 - **manaStore.ts**: Mana gathering, elements, conversion
 - **combatStore.ts**: Combat system, spells, floor progression
@@ -1091,6 +1093,14 @@ The codebase has been refactored into a modular architecture for better maintain
 - **skillStore.ts**: Skill state, studying, evolution
 - **uiStore.ts**: UI state, modals, debug settings
 
+**Legacy Store (Migration in Progress):**
+- **store.ts**: Legacy monolithic store (reduced from ~2812 lines to ~14KB)
+- **store/**: Legacy store slices being migrated to `stores/`
+  - `combatSlice.ts`, `manaSlice.ts`, `skillSlice.ts`, etc.
+  - `computed.ts`: Computed stats utilities
+- **store-modules/**: Legacy store utilities
+  - `computed-stats.ts`, `initial-state.ts`, `tick-logic.ts`, etc.
+
 #### Crafting System (`src/lib/game/crafting-actions/`)
 - Modular action files for each crafting stage
 - Design, preparation, application, equipment, disenchant actions