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/AgentIndicator.svelte

@@ -1,10 +1,10 @@
 <script lang="ts">
-  import type { ToolCallResult } from '$lib/stores/chat'
+  import type { ActivityEntry } from '$lib/stores/chat'
   import LoaderCircleIcon from '@lucide/svelte/icons/loader-circle'
   import CheckIcon from '@lucide/svelte/icons/check'
   import XIcon from '@lucide/svelte/icons/x'
 
-  let { active = false, lastTool = null as ToolCallResult | null, error = '' }: { active?: boolean; lastTool?: ToolCallResult | null; error?: string } = $props()
+  let { active = false, lastActivity = null as ActivityEntry | null, error = '' }: { active?: boolean; lastActivity?: ActivityEntry | null; error?: string } = $props()
 
   let done = $state(false)
   let wasActive = $state(false)
@@ -13,7 +13,6 @@
     if (active) { done = false; wasActive = true }
     if (!active && wasActive) {
       done = true
-      // Fade out after 3s
       const t = setTimeout(() => { done = false; wasActive = false }, 3000)
       return () => clearTimeout(t)
     }
@@ -22,33 +21,8 @@
   const label = $derived.by(() => {
     if (error) return error
     if (!active && done) return 'Done'
-    if (!lastTool) return 'Agent is thinking…'
-    const args = lastTool.args ?? {}
-    switch (lastTool.name) {
-      case 'set_goal': return 'Setting goal…'
-      case 'propose_plan': return 'Building plan…'
-      case 'search_knowledge': return `Researching: ${args.query ?? ''}`
-      case 'get_entity': return `Looking up ${args.slug_or_id ?? ''}`
-      case 'get_entity_knowledge': return `Checking prior knowledge…`
-      case 'get_relations': return `Checking relationships…`
-      case 'list_lxcs': return 'Listing containers…'
-      case 'list_entities': return 'Listing entities…'
-      case 'get_health_summary': return 'Checking fleet health…'
-      case 'run': {
-        const purpose = args.purpose ?? ''
-        const target = args.target ?? ''
-        if (purpose) return purpose
-        if (target) return `Running on ${target}…`
-        return 'Running command…'
-      }
-      case 'get_execution_status': return 'Checking execution status…'
-      case 'update_plan_step': return 'Updating progress…'
-      case 'upsert_knowledge': return 'Recording knowledge…'
-      case 'complete_task': return 'Wrapping up…'
-      case 'ping_service': return 'Checking service…'
-      case 'ask_operator': return 'Asking operator…'
-      default: return `${lastTool.name}…`
-    }
+    if (lastActivity) return lastActivity.description
+    return 'Agent is thinking…'
   })
 </script>