sidebar activity timeline replaces tool display in chat

- New ActivityTimeline: unified timeline in sidebar showing all agent actions
  (goal, plan steps, tool calls, knowledge, completion) in reverse chron order
- activityLog derived store merges messages + planSteps + currentTask
- AgentIndicator stays in chat (thinking/working indicator), simplified props
- ToolCallGroup removed from chat — tools visible only in sidebar timeline
- SessionDigest replaced by ActivityTimeline
- PlanProgress restored in sidebar (conceptual steps, separate from timeline)

web/src/lib/components/TaskContextPanel.svelte

@@ -2,26 +2,22 @@
   import { onMount } from 'svelte'
   import { startWorkspace } from '$lib/stores/workspace'
   import GoalHeader from './GoalHeader.svelte'
+  import PlanProgress from './PlanProgress.svelte'
   import OperatorQuestion from './OperatorQuestion.svelte'
   import SessionGraph from './SessionGraph.svelte'
-  import SessionDigest from './SessionDigest.svelte'
+  import ActivityTimeline from './ActivityTimeline.svelte'
 
   onMount(() => startWorkspace())
 </script>
 
-<!--
-  The task's live control panel: goal + status, plan progress, a pinned
-  question when the agent needs a decision, the live entity graph (pulses what
-  the agent is touching, flags health changes), and the outcome/knowledge
-  record once the task completes. Driven by the always-on events stream
-  (see workspace.ts) so it keeps updating during server-side auto-continuation,
-  not just while a chat turn is streaming.
--->
 <div class="flex h-full min-h-0 flex-col">
   <GoalHeader />
+  <PlanProgress />
   <OperatorQuestion />
   <div class="min-h-0 flex-1">
     <SessionGraph />
   </div>
-  <SessionDigest />
+  <div class="max-h-[40%] overflow-y-auto border-t">
+    <ActivityTimeline />
+  </div>
 </div>