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/pages/Chat.svelte

@@ -1,9 +1,8 @@
 <script lang="ts">
-  import { messages, streaming, connectionState, currentSession, sendMessage, cancelStream, reconnect, error, chatErrors, dismissError, toolTimeline } from '$lib/stores/chat'
+  import { messages, streaming, connectionState, currentSession, sendMessage, cancelStream, reconnect, error, chatErrors, dismissError, activityLog } from '$lib/stores/chat'
   import { currentTask } from '$lib/stores/workspace'
   import SessionRail from '$lib/components/SessionRail.svelte'
   import TaskContextPanel from '$lib/components/TaskContextPanel.svelte'
-  import ToolCallGroup from '$lib/components/ToolCallGroup.svelte'
   import InlineApproval from '$lib/components/InlineApproval.svelte'
   import AgentIndicator from '$lib/components/AgentIndicator.svelte'
   import { getToolRenderer } from '$lib/tool-renderers'
@@ -53,11 +52,6 @@
     return matched.slice(0, MAX_INLINE_CARDS)
   }
 
-  function getRemaining(msg: { tools: any[] }, inline: any[]): any[] {
-    const inlineIds = new Set(inline.map((t) => t.id))
-    return msg.tools.filter((t) => !inlineIds.has(t.id))
-  }
-
   // Resizable right rail (session graph). Persisted so it survives reloads.
   const RAIL_MIN = 260
   const RAIL_MAX = 620
@@ -158,11 +152,6 @@
                     <renderer.component {tool} />
                   {/if}
                 {/each}
-                <ToolCallGroup
-                  tools={msg.tools}
-                  unmatched={getRemaining(msg, getInlineTools(msg))}
-                  active={$streaming && i === $messages.length - 1}
-                />
                 {#if msg.text}
                   <div class="prose-chat max-w-none text-sm leading-relaxed">
                     <!-- eslint-disable-next-line svelte/no-at-html-tags — sanitized via DOMPurify -->
@@ -178,7 +167,7 @@
         {/each}
         <AgentIndicator
           active={$streaming || liveStatus === 'executing'}
-          lastTool={$toolTimeline.filter((t) => t.type === 'tool_use').at(-1) ?? null}
+          lastActivity={$activityLog.find((e) => e.status === 'running') ?? null}
           error={$error}
         />
         <div bind:this={messagesEnd}></div>