perf: optimize /api/sessions endpoint response payload

Slim down SessionSummary responses to reduce payload size:
- Replace full todos array with computed todoProgress summary
- Replace metadata object with only necessary fields (name, path, summary.text)
- Remove unused fields (thinking, createdAt, permissionMode, modelMode)
- Refactor sorting to work on full Session objects before mapping

This significantly reduces /api/sessions response size, especially for
sessions with many todos or tools.

web/src/components/SessionList.tsx

@@ -58,11 +58,9 @@ function getSessionTitle(session: SessionSummary): string {
 }
 
 function getTodoProgress(session: SessionSummary): { completed: number; total: number } | null {
-    if (!session.todos || session.todos.length === 0) return null
-    const total = session.todos.length
-    const completed = session.todos.filter(t => t.status === 'completed').length
-    if (completed === total) return null
-    return { completed, total }
+    if (!session.todoProgress) return null
+    if (session.todoProgress.completed === session.todoProgress.total) return null
+    return session.todoProgress
 }
 
 export function SessionList(props: {

web/src/types/api.ts

@@ -58,16 +58,18 @@ export type Session = {
     modelMode?: ModelMode
 }
 
+export type SessionSummaryMetadata = {
+    name?: string
+    path: string
+    summary?: { text: string }
+}
+
 export type SessionSummary = {
     id: string
     active: boolean
-    thinking: boolean
     updatedAt: number
-    createdAt: number
-    permissionMode: PermissionMode
-    modelMode: ModelMode
-    metadata: SessionMetadataSummary | null
-    todos?: TodoItem[]
+    metadata: SessionSummaryMetadata | null
+    todoProgress: { completed: number; total: number } | null
     pendingRequestsCount: number
 }