feat(sidebar): replicate WorkBuddy task context menu (TODO 01)

Replace the sidebar delete button with the original task menu: pin/unpin,
rename, open in a separate window, open folder, archive and delete.

Source: REA ev_f5e9d71a676c453daab40928acfb33aeabae68ba57ffda342380cead7f1a1fe2
(WorkBuddy 5.8.3 task menu, open state) supplies the container/item geometry,
the two dividers, danger colour and every item icon.

Verified by scripts/verify-task-menu.cjs: 33 assertions in a real isolated
Electron app (real preload/IPC/filesystem), including menu geometry, anchor
offset, pin/rename/archive persistence, open-folder target and the separate
window query. typecheck, test:conversation and build pass.

src/main/sessions.ts

@@ -93,8 +93,40 @@ async function persist(): Promise<void> {
 export async function listSessions(): Promise<SessionMeta[]> {
   const store = await load()
   return [...store.sessions]
-    .sort((a, b) => b.updatedAt - a.updatedAt)
-    .map(({ id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: mode, thinkingLevel: level }) => ({ id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: agentMode(mode), thinkingLevel: level }))
+    // 置顶任务优先（最近置顶在前），其余按更新时间倒序。
+    .sort((a, b) => Number(b.pinnedAt ?? 0) - Number(a.pinnedAt ?? 0) || b.updatedAt - a.updatedAt)
+    .map(({ id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: mode, thinkingLevel: level, pinnedAt, archivedAt }) => ({ id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: agentMode(mode), thinkingLevel: level, pinnedAt, archivedAt }))
+}
+
+/** 侧栏可见任务：默认排除已归档；`includeArchived` 供归档视图使用。 */
+export async function listVisibleSessions(includeArchived = false): Promise<SessionMeta[]> {
+  const sessions = await listSessions()
+  return includeArchived ? sessions : sessions.filter((session) => session.archivedAt === undefined)
+}
+
+export async function setSessionPinned(sessionId: string, pinned: boolean): Promise<SessionMeta> {
+  const store = await load()
+  const session = store.sessions.find((item) => item.id === sessionId)
+  if (!session) throw new Error('会话不存在')
+  const previous = session.pinnedAt
+  session.pinnedAt = pinned ? Date.now() : undefined
+  try { await persist() } catch (error) { session.pinnedAt = previous; throw error }
+  return meta(session)
+}
+
+export async function setSessionArchived(sessionId: string, archived: boolean): Promise<SessionMeta> {
+  const store = await load()
+  const session = store.sessions.find((item) => item.id === sessionId)
+  if (!session) throw new Error('会话不存在')
+  const previous = session.archivedAt
+  session.archivedAt = archived ? Date.now() : undefined
+  try { await persist() } catch (error) { session.archivedAt = previous; throw error }
+  return meta(session)
+}
+
+function meta(session: SessionRecord): SessionMeta {
+  const { id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: mode, thinkingLevel: level, pinnedAt, archivedAt } = session
+  return { id, title, createdAt, updatedAt, workspaceId, cwd, modelId, expertId, agentMode: agentMode(mode), thinkingLevel: level, pinnedAt, archivedAt }
 }
 
 export async function createSession(title = '新对话', context: SessionContext = {}): Promise<SessionMeta> {