feat: handle mid-stream LLM resets and deduplicate UI action stream events

- Backend (LLM Gateway):
  - Record structured 'llm_stream_reset' event with discard action, failure reason, and retry messaging on mid-stream generation errors.
  - Add unit test verifying stream reset event payload on mid-stream errors.

- Frontend (Showcase UI):
  - Handle 'llm_stream_reset' events in agent service and stream aggregator, discarding interrupted chunks while showing retry indicators.
  - Establish a single source of truth for tool and action events in the timeline to eliminate duplicated action rows while retaining ADB and explorer tools.
  - Add @angular/cdk dependency and update agent stream component styling and layout.
  - Add unit tests for stream aggregation and tool display filtering.

apps/showcase_ui/src/app/utils/tool-formatter.util.ts

@@ -15,7 +15,6 @@
  */
 
 import { ActionParam } from '../core/models/stream.model';
-import { isAndroidAction, isReportStatusAction } from './action-formatter.util';
 import { extractNumbersFromCoordinateValue, isPureDirectionString, parseSequenceCoordinates } from './image-overlay.util';
 
 // Tool objects are replaced (not mutated) when a trace is updated, so a
@@ -276,24 +275,12 @@ export function isInternalPlumbingTool(tool: any): boolean {
 /**
  * Determines whether a tool invocation should be displayed in the timeline.
  */
-export function shouldShowTool(tool: any, stepData?: any): boolean {
+export function shouldShowTool(tool: any, _stepData?: any): boolean {
   if (!tool || !tool.name) return false;
   if (tool.type === 'llm_call') return false;
   if (tool.type === 'agent') return false;
   if (isInternalPlumbingTool(tool)) return false;
 
-  // If this tool is an operator/validator atomic action that duplicates stepData.action_taken, skip it
-  if (stepData && stepData.action_taken && isAndroidAction(stepData.action_taken) && isDeviceActionTool(tool)) {
-    const agentName = (tool.agent_name || tool.agent || '').toLowerCase();
-    const isSelfHealingOrSubAgent = agentName.includes('failure') || 
-                                    agentName.includes('analyzer') || 
-                                    agentName.includes('diagnos') || 
-                                    (agentName && agentName !== 'operator' && agentName !== 'flashrunner' && agentName !== 'validator');
-    if (!isSelfHealingOrSubAgent) {
-      return false;
-    }
-  }
-
   return true;
 }