tool timeline in sidebar + compact chat tools + scroll fixes

- SessionDigest now includes live tool timeline, plan steps, knowledge
- ToolCallGroup compact: single-line with collapsible names only (no JSON)
- Activity bar moved to bottom of messages, smart scroll respects user position
- setGoal now sets status=executing (removed stuck planning state)
- PlanProgress merged into SessionDigest, removed from TaskContextPanel
- New toolTimeline derived store in chat.ts

web/src/lib/stores/chat.ts

@@ -1,4 +1,4 @@
-import { writable, get } from 'svelte/store'
+import { writable, derived, get } from 'svelte/store'
 import { streamChat, fetchSessions, fetchMessages, deleteSession as apiDeleteSession } from '$lib/api'
 import type { ChatEvent, Session, Message } from '$lib/api'
 
@@ -81,6 +81,36 @@ export function addChatError(message: string, action?: string) {
   chatErrors.update((e) => [...e, { id: crypto.randomUUID(), message, action }])
 }
 
+// ToolTimelineEntry — one tool call from the chat transcript, flattened for
+// the sidebar activity timeline. Derived from messages in real time.
+export interface ToolTimelineEntry {
+  id: string
+  name: string
+  args?: any
+  result?: any
+  error?: string
+  type: 'tool_use' | 'tool_result'
+  msgIndex: number // which message this tool belongs to
+}
+
+export const toolTimeline = derived(messages, ($msgs) => {
+  const entries: ToolTimelineEntry[] = []
+  for (let i = 0; i < $msgs.length; i++) {
+    for (const t of $msgs[i].tools) {
+      entries.push({
+        id: t.id ?? crypto.randomUUID(),
+        name: t.name,
+        args: t.args,
+        result: t.result,
+        error: t.error,
+        type: t.type,
+        msgIndex: i
+      })
+    }
+  }
+  return entries
+})
+
 // Per-session controller tracking. Multiple tasks can stream concurrently
 // (see sendMessage's session guard above this used to be a single global
 // `activeController`, which meant cancelStream()/newChat() always aborted