refactor(agents): drop transcript compact mode and simplify row spacing

- Remove the compact layout prop from AgentSessionTranscriptList,
  ManagedAgentSessionPanel, and AgentSessionThreadPanel; always render the
  tighter transcript density
- Revert consecutive tool-call grouping (tool_group segments, ToolCallGroup,
  segment spacing helpers) and render each tool as a normal transcript row
- Add symmetric per-type row spacing: my-2.5 for messages, my-1 for tools,
  my-2 for other items
- Simplify ToolItem wrapper padding now that grouped/compact props are gone

Author: tellaho

desktop/src/features/agents/ui/AgentSessionToolItem.tsx

@@ -10,12 +10,8 @@ import { buildCompactToolSummary } from "./agentSessionToolSummary";
 import { asRecord, formatCodeValue, formatDuration } from "./agentSessionUtils";
 
 export function ToolItem({
-  compact = false,
-  grouped = false,
   item,
 }: {
-  compact?: boolean;
-  grouped?: boolean;
   item: Extract<TranscriptItem, { type: "tool" }>;
 }) {
   const [isExpanded, setIsExpanded] = React.useState(false);
@@ -34,11 +30,7 @@ export function ToolItem({
 
   return (
     <div
-      className={cn(
-        "not-prose w-full",
-        compact ? "px-0" : "px-1",
-        grouped ? "py-0" : compact ? "py-0.5" : "py-0.5",
-      )}
+      className="not-prose w-full px-0 py-0.5"
       data-testid="transcript-tool-item"
     >
       <details