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/state.js

@@ -0,0 +1,168 @@
+/**
+ * Core State Management Module
+ * Centralizes all extension state variables
+ */
+
+/**
+ * Extension settings - persisted to SillyTavern settings
+ */
+export let extensionSettings = {
+    enabled: true,
+    autoUpdate: true,
+    updateDepth: 4, // How many messages to include in the context
+    generationMode: 'together', // 'separate' or 'together' - whether to generate with main response or separately
+    showUserStats: true,
+    showInfoBox: true,
+    showCharacterThoughts: true,
+    showThoughtsInChat: true, // Show thoughts overlay in chat
+    enableHtmlPrompt: false, // Enable immersive HTML prompt injection
+    enablePlotButtons: true, // Show plot progression buttons above chat input
+    panelPosition: 'right', // 'left', 'right', or 'top'
+    theme: 'default', // Theme: default, sci-fi, fantasy, cyberpunk, custom
+    customColors: {
+        bg: '#1a1a2e',
+        accent: '#16213e',
+        text: '#eaeaea',
+        highlight: '#e94560'
+    },
+    statBarColorLow: '#cc3333', // Color for low stat values (red)
+    statBarColorHigh: '#33cc66', // Color for high stat values (green)
+    enableAnimations: true, // Enable smooth animations for stats and content updates
+    mobileFabPosition: {
+        top: 'calc(var(--topBarBlockSize) + 60px)',
+        right: '12px'
+    }, // Saved position for mobile FAB button
+    userStats: {
+        health: 100,
+        satiety: 100,
+        energy: 100,
+        hygiene: 100,
+        arousal: 0,
+        mood: '😐',
+        conditions: 'None',
+        inventory: 'None'
+    },
+    classicStats: {
+        str: 10,
+        dex: 10,
+        con: 10,
+        int: 10,
+        wis: 10,
+        cha: 10
+    },
+    lastDiceRoll: null // Store last dice roll result
+};
+
+/**
+ * Last generated data from AI response
+ */
+export let lastGeneratedData = {
+    userStats: null,
+    infoBox: null,
+    characterThoughts: null,
+    html: null
+};
+
+/**
+ * Tracks the "committed" tracker data that should be used as source for next generation
+ * This gets updated when user sends a new message or first time generation
+ */
+export let committedTrackerData = {
+    userStats: null,
+    infoBox: null,
+    characterThoughts: null
+};
+
+/**
+ * Tracks whether the last action was a swipe (for separate mode)
+ * Used to determine whether to commit lastGeneratedData to committedTrackerData
+ */
+export let lastActionWasSwipe = false;
+
+/**
+ * Flag indicating if generation is in progress
+ */
+export let isGenerating = false;
+
+/**
+ * Tracks if we're currently doing a plot progression
+ */
+export let isPlotProgression = false;
+
+/**
+ * Temporary storage for pending dice roll (not saved until user clicks "Save Roll")
+ */
+export let pendingDiceRoll = null;
+
+/**
+ * Fallback avatar image (base64-encoded SVG with "?" icon)
+ * Using base64 to avoid quote-encoding issues in HTML attributes
+ */
+export const FALLBACK_AVATAR_DATA_URI = 'data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMDAiIGhlaWdodD0iMTAwIj48cmVjdCB3aWR0aD0iMTAwIiBoZWlnaHQ9IjEwMCIgZmlsbD0iI2NjY2NjYyIgb3BhY2l0eT0iMC4zIi8+PHRleHQgeD0iNTAlIiB5PSI1MCUiIHRleHQtYW5jaG9yPSJtaWRkbGUiIGR5PSIuM2VtIiBmaWxsPSIjNjY2IiBmb250LXNpemU9IjQwIj4/PC90ZXh0Pjwvc3ZnPg==';
+
+/**
+ * UI Element References (jQuery objects)
+ */
+export let $panelContainer = null;
+export let $userStatsContainer = null;
+export let $infoBoxContainer = null;
+export let $thoughtsContainer = null;
+
+/**
+ * State setters - provide controlled mutation of state variables
+ */
+export function setExtensionSettings(newSettings) {
+    extensionSettings = newSettings;
+}
+
+export function updateExtensionSettings(updates) {
+    Object.assign(extensionSettings, updates);
+}
+
+export function setLastGeneratedData(data) {
+    lastGeneratedData = data;
+}
+
+export function updateLastGeneratedData(updates) {
+    Object.assign(lastGeneratedData, updates);
+}
+
+export function setCommittedTrackerData(data) {
+    committedTrackerData = data;
+}
+
+export function updateCommittedTrackerData(updates) {
+    Object.assign(committedTrackerData, updates);
+}
+
+export function setLastActionWasSwipe(value) {
+    lastActionWasSwipe = value;
+}
+
+export function setIsGenerating(value) {
+    isGenerating = value;
+}
+
+export function setIsPlotProgression(value) {
+    isPlotProgression = value;
+}
+
+export function setPendingDiceRoll(roll) {
+    pendingDiceRoll = roll;
+}
+
+export function setPanelContainer($element) {
+    $panelContainer = $element;
+}
+
+export function setUserStatsContainer($element) {
+    $userStatsContainer = $element;
+}
+
+export function setInfoBoxContainer($element) {
+    $infoBoxContainer = $element;
+}
+
+export function setThoughtsContainer($element) {
+    $thoughtsContainer = $element;
+}