發佈 0.1.12：會話模式新增「每則獨立」，ctx 達 80% 自動開新會話

根本原因：
會話越用越慢——每張生成圖都會塞回上下文，實測同一會話從 36 秒
一路漲到 135 秒，也更容易在串流時被切斷。

修法：
1. 會話模式 sharedSession 布林改為 sessionMode（per-chat / shared / stateless），
   stateless = 每則訊息獨立、不保留記憶，適合單張生圖這類不需上下文的 bot；
   舊設定檔的 sharedSession 自動相容轉換。
2. 新增 autoResetCtxPercent（預設 80）：任一會話上下文用量達門檻即自動
   開新會話並在回覆末尾提示，避免無限累積。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/registry.js

@@ -78,7 +78,7 @@ async function listBots() {
       sandbox: cfg?.sandbox || null,
       model: cfg?.model || '',
       reasoningEffort: cfg?.reasoningEffort || '',
-      sharedSession: !!cfg?.sharedSession,
+      sessionMode: cfg?.sessionMode || 'per-chat',
       networkAccess: !!cfg?.networkAccess,
       serviceTier: cfg?.serviceTier || '',
       timeoutMinutes: cfg?.timeoutMinutes || null,
@@ -114,7 +114,7 @@ function validateBotInput({ name, token, workDir, sandbox }, { isCreate }) {
   }
 }
 
-async function createBot({ name, token, workDir, sandbox, model, reasoningEffort, sharedSession, networkAccess, timeoutMinutes }) {
+async function createBot({ name, token, workDir, sandbox, model, reasoningEffort, sessionMode, networkAccess, timeoutMinutes }) {
   validateBotInput({ name, token, workDir, sandbox }, { isCreate: true });
   const reg = loadRegistry();
   if (reg.bots[name]) throw new Error(`已有同名 bot：${name}`);
@@ -130,7 +130,7 @@ async function createBot({ name, token, workDir, sandbox, model, reasoningEffort
     sandbox: sandbox || 'workspace-write',
     model: model || '',
     reasoningEffort: reasoningEffort || '',
-    sharedSession: !!sharedSession,
+    sessionMode: ['per-chat','shared','stateless'].includes(sessionMode) ? sessionMode : 'per-chat',
     networkAccess: !!networkAccess,
     serviceTier: 'priority', // 速度固定 Fast 1.5x
     timeoutMinutes: Number(timeoutMinutes) || 30,
@@ -162,7 +162,7 @@ async function updateBot(name, patch) {
   }
   if (patch.model !== undefined) raw.model = patch.model;
   if (patch.reasoningEffort !== undefined) raw.reasoningEffort = patch.reasoningEffort;
-  if (patch.sharedSession !== undefined) raw.sharedSession = !!patch.sharedSession;
+  if (['per-chat','shared','stateless'].includes(patch.sessionMode)) { raw.sessionMode = patch.sessionMode; delete raw.sharedSession; }
   if (patch.networkAccess !== undefined) raw.networkAccess = !!patch.networkAccess;
   if (patch.timeoutMinutes !== undefined && Number(patch.timeoutMinutes) > 0) {
     raw.timeoutMinutes = Number(patch.timeoutMinutes);