feat: global activity feed + session digest

Ops "Executions" tab showed raw target UUIDs, alphabetical (not
recency) order, and a stale status vocabulary from an earlier schema
iteration — never actually usable as a live "what's happening" view.
Replaced with a new recency-ordered /api/v1/activity/recent endpoint
and matching table (human-readable action summaries, risk/status
badges, duration, inline error preview).

Also added /api/v1/activity/session/{id} + a collapsible SessionDigest
panel in the chat rail, answering "what did this session actually do"
(executions by status, entities touched, knowledge written) — the
missing piece for proactive outcome reporting to be visible in the UI,
not just in the chat transcript.

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

web/src/lib/api.ts

@@ -242,6 +242,41 @@ export async function cancelExecution(id: string): Promise<Execution | null> {
   return res.json()
 }
 
+export interface ActivityItem {
+  id: string
+  target: string
+  verb: string
+  summary: string
+  risk_class: string
+  status: string
+  duration_ms: number | null
+  error?: string
+  created_at: string
+  completed_at: string | null
+}
+
+export async function fetchRecentActivity(limit = 50): Promise<ActivityItem[]> {
+  const res = await fetch(`${API}/activity/recent?limit=${limit}`)
+  if (!res.ok) return []
+  const data = await res.json()
+  return data.items ?? []
+}
+
+export interface SessionDigest {
+  session_id: string
+  total_executions: number
+  by_status: Record<string, number>
+  entities_touched: string[]
+  executions: { target: string; verb: string; summary: string; risk_class: string; status: string }[]
+  knowledge_created: string[]
+}
+
+export async function fetchSessionDigest(sessionId: string): Promise<SessionDigest | null> {
+  const res = await fetch(`${API}/activity/session/${sessionId}`)
+  if (!res.ok) return null
+  return res.json()
+}
+
 export interface Signal {
   id: string
   slug: string