fix(growth): MEDIUM-10 Experience 添加 tool_used 字段

根因: Experience 结构体没有 tool_used 字段，PatternAggregator 从
context 字段提取工具名（语义混淆），导致工具信息不准确。

修复:
- experience_store.rs: Experience 添加 tool_used: Option<String> 字段
  (#[serde(default)] 兼容旧数据)，Experience::new() 初始化为 None
- experience_extractor.rs: persist_experiences() 从 ExperienceCandidate
  的 tools_used[0] 填充 tool_used，同时填充 industry_context
- pattern_aggregator.rs: 改用 tool_used 字段提取工具名，不再误用 context
- store_experience() 将 tool_used 加入 keywords 提升搜索命中率

crates/zclaw-growth/src/experience_extractor.rs

@@ -45,13 +45,16 @@ impl ExperienceExtractor {
                 Outcome::Partial => "partial",
                 Outcome::Failed => "failed",
             };
-            let exp = crate::experience_store::Experience::new(
+            let mut exp = crate::experience_store::Experience::new(
                 agent_id,
                 &candidate.pain_pattern,
                 &candidate.context,
                 candidate.solution_steps.clone(),
                 outcome_str,
             );
+            // 填充 tool_used：取 tools_used 中的第一个作为主要工具
+            exp.tool_used = candidate.tools_used.first().cloned();
+            exp.industry_context = candidate.industry_context.clone();
             store.store_experience(&exp).await?;
             count += 1;
         }