Major refactor: security, performance, and code organization

Security:
- DeepSeek API moved to server-side proxy with rate limiting (20 req/min)
- Whitelist validation for all POST/PUT routes
- Cookie security (secure, sameSite, httpOnly in production)
- Input validation for messages, tokens, temperature
- Sanitized hasOwnProperty to prevent prototype pollution

Performance:
- Lazy loading for chat messages (sliding window of 20)
- Streaming response throttling (50ms batches)
- Scroll optimization (only scroll on new messages)
- AbortController fix for stop button

Code organization:
- GamePage refactored from ~1170 to ~750 lines
- New hooks: useGameSession, useStreamingResponse, useCharacterDetection, useLazyMessages
- New components: MessageList, ChatInput, SessionSelector, CharacterPanel
- Fixed ESLint errors

Features:
- OOC mode button for direct AI instructions
- Message versions (aiResponse) now persist to DB
- playerId saved in sessions

src/pages/GamePage.css

@@ -289,6 +289,28 @@
   box-sizing: border-box;
 }
 
+.load-more-messages-btn {
+  align-self: center;
+  padding: 0.5rem 1rem;
+  margin-bottom: 0.5rem;
+  background: rgba(255, 255, 255, 0.08);
+  border: 1px solid rgba(255, 255, 255, 0.15);
+  border-radius: 20px;
+  color: rgba(255, 255, 255, 0.7);
+  font-size: 0.85rem;
+  cursor: pointer;
+  transition: all 0.2s ease;
+}
+
+.load-more-messages-btn:hover {
+  background: rgba(255, 255, 255, 0.12);
+  color: rgba(255, 255, 255, 0.9);
+}
+
+.load-more-messages-btn:active {
+  transform: scale(0.98);
+}
+
 .message {
   max-width: 88%;
   animation: fadeIn 0.25s ease;
@@ -710,6 +732,48 @@
   background: #b91c1c;
 }
 
+/* OOC Mode Button */
+.ooc-btn {
+  padding: 0.4rem 0.6rem;
+  background: transparent;
+  border: 1px solid rgba(255, 255, 255, 0.2);
+  border-radius: 12px;
+  color: #888;
+  font-size: 0.7rem;
+  font-weight: 600;
+  cursor: pointer;
+  transition: all 0.2s;
+  flex-shrink: 0;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.ooc-btn:hover {
+  background: rgba(255, 255, 255, 0.1);
+  color: #aaa;
+}
+
+.ooc-btn.active {
+  background: #f59e0b;
+  border-color: #f59e0b;
+  color: #000;
+}
+
+.ooc-btn.active:hover {
+  background: #d97706;
+  border-color: #d97706;
+}
+
+/* OOC Mode Input Container */
+.input-container.ooc-mode {
+  border-color: #f59e0b;
+  background: rgba(245, 158, 11, 0.1);
+}
+
+.input-container.ooc-mode textarea::placeholder {
+  color: #f59e0b;
+}
+
 /* Streaming message animation */
 .message.streaming .message-text {
   position: relative;