feat: step artifacts framework

- Add Artifact type to Step (name, path, artifact_type, description)
- step_done tool accepts optional artifacts parameter
- Save artifacts to step_artifacts DB table
- Display artifacts in frontend PlanSection (tag style)
- Show artifacts in step context for sub-agents and coordinator
- Add LLM client retry with exponential backoff

web/src/components/PlanSection.vue

@@ -59,6 +59,11 @@ function quoteStep(e: Event, step: PlanStepInfo) {
         <div v-if="step.command && expandedSteps.has(step.order)" class="step-detail">
           {{ step.command }}
         </div>
+        <div v-if="step.artifacts?.length" class="step-artifacts">
+          <span v-for="a in step.artifacts" :key="a.path" class="artifact-tag">
+            📄 {{ a.name }} <span class="artifact-type">{{ a.artifact_type }}</span>
+          </span>
+        </div>
       </div>
       <div v-if="!steps.length" class="empty-state">
         AI 将在这里展示执行计划
@@ -188,6 +193,30 @@ function quoteStep(e: Event, step: PlanStepInfo) {
   border-top: 1px solid var(--border);
 }
 
+.step-artifacts {
+  padding: 4px 10px 8px 44px;
+  display: flex;
+  flex-wrap: wrap;
+  gap: 4px;
+}
+
+.artifact-tag {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  font-size: 11px;
+  color: var(--text-secondary);
+  background: var(--bg-tertiary);
+  padding: 2px 8px;
+  border-radius: 4px;
+}
+
+.artifact-type {
+  font-size: 10px;
+  color: var(--accent);
+  opacity: 0.8;
+}
+
 .empty-state {
   color: var(--text-secondary);
   font-size: 13px;

web/src/types.ts

@@ -26,11 +26,19 @@ export interface ExecutionLogEntry {
   created_at: string
 }
 
+export interface StepArtifact {
+  name: string
+  path: string
+  artifact_type: string
+  description: string
+}
+
 export interface PlanStepInfo {
   order: number
   description: string
   command: string
   status?: 'pending' | 'running' | 'done' | 'failed'
+  artifacts?: StepArtifact[]
 }
 
 export interface Comment {