refactor(core): extract core modules (state, persistence, config, events)

Extract core system modules from monolithic index.js into modular architecture:

- src/core/state.js: All extension state variables with controlled setters
- src/core/persistence.js: Settings and chat data persistence functions
- src/core/config.js: Extension metadata and default configuration
- src/core/events.js: SillyTavern event system wrapper

Updated index.js to import and use new core modules.
Removed ~220 lines of state/persistence code from index.js.

Part of Epic 1: Foundation & Core Systems (Phase 1.1-1.2)

src/core/persistence.js

@@ -0,0 +1,140 @@
+/**
+ * Core Persistence Module
+ * Handles saving/loading extension settings and chat data
+ */
+
+import { saveSettingsDebounced, chat_metadata, saveChatDebounced } from '../../../../../../script.js';
+import { power_user } from '../../../../../power-user.js';
+import { getContext } from '../../../../../extensions.js';
+import {
+    extensionSettings,
+    lastGeneratedData,
+    setExtensionSettings,
+    updateExtensionSettings,
+    setLastGeneratedData
+} from './state.js';
+
+const extensionName = 'third-party/rpg-companion-sillytavern';
+
+/**
+ * Loads the extension settings from the global settings object.
+ */
+export function loadSettings() {
+    if (power_user.extensions && power_user.extensions[extensionName]) {
+        updateExtensionSettings(power_user.extensions[extensionName]);
+        // console.log('[RPG Companion] Settings loaded:', extensionSettings);
+    } else {
+        // console.log('[RPG Companion] No saved settings found, using defaults');
+    }
+}
+
+/**
+ * Saves the extension settings to the global settings object.
+ */
+export function saveSettings() {
+    if (!power_user.extensions) {
+        power_user.extensions = {};
+    }
+    power_user.extensions[extensionName] = extensionSettings;
+    saveSettingsDebounced();
+}
+
+/**
+ * Saves RPG data to the current chat's metadata.
+ */
+export function saveChatData() {
+    if (!chat_metadata) {
+        return;
+    }
+
+    chat_metadata.rpg_companion = {
+        userStats: extensionSettings.userStats,
+        classicStats: extensionSettings.classicStats,
+        lastGeneratedData: lastGeneratedData,
+        timestamp: Date.now()
+    };
+
+    saveChatDebounced();
+}
+
+/**
+ * Updates the last assistant message's swipe data with current tracker data.
+ * This ensures user edits are preserved across swipes and included in generation context.
+ */
+export function updateMessageSwipeData() {
+    const chat = getContext().chat;
+    if (!chat || chat.length === 0) {
+        return;
+    }
+
+    // Find the last assistant message
+    for (let i = chat.length - 1; i >= 0; i--) {
+        const message = chat[i];
+        if (!message.is_user) {
+            // Found last assistant message - update its swipe data
+            if (!message.extra) {
+                message.extra = {};
+            }
+            if (!message.extra.rpg_companion_swipes) {
+                message.extra.rpg_companion_swipes = {};
+            }
+
+            const swipeId = message.swipe_id || 0;
+            message.extra.rpg_companion_swipes[swipeId] = {
+                userStats: lastGeneratedData.userStats,
+                infoBox: lastGeneratedData.infoBox,
+                characterThoughts: lastGeneratedData.characterThoughts
+            };
+
+            // console.log('[RPG Companion] Updated message swipe data after user edit');
+            break;
+        }
+    }
+}
+
+/**
+ * Loads RPG data from the current chat's metadata.
+ */
+export function loadChatData() {
+    if (!chat_metadata || !chat_metadata.rpg_companion) {
+        // Reset to defaults if no data exists
+        updateExtensionSettings({
+            userStats: {
+                health: 100,
+                satiety: 100,
+                energy: 100,
+                hygiene: 100,
+                arousal: 0,
+                mood: '😐',
+                conditions: 'None',
+                inventory: 'None'
+            }
+        });
+        setLastGeneratedData({
+            userStats: null,
+            infoBox: null,
+            characterThoughts: null,
+            html: null
+        });
+        return;
+    }
+
+    const savedData = chat_metadata.rpg_companion;
+
+    // Restore stats
+    if (savedData.userStats) {
+        extensionSettings.userStats = { ...savedData.userStats };
+    }
+
+    // Restore classic stats
+    if (savedData.classicStats) {
+        extensionSettings.classicStats = { ...savedData.classicStats };
+    }
+
+    // Restore last generated data
+    if (savedData.lastGeneratedData) {
+        setLastGeneratedData({ ...savedData.lastGeneratedData });
+    }
+
+    // console.log('[RPG Companion] Loaded chat data:', savedData);
+}