优化: 立项回滚级联删 + df-ideas 死代码清理

- T-09: idea.rs:149 立项失败回滚 delete→purge_with_descendants（防孤儿子记录）
- T-12: capture.rs 删 CaptureInput/IdeaCapture 死代码，保留 Idea/IdeaScores 共享实体
- T-10: 无改动（normalize_path 已含 canonicalize，判定已解决）

crates/df-ideas/src/capture.rs

@@ -1,26 +1,9 @@
-//! 想法捕获 — 快速记录与管理
+//! 想法实体与评分类型 — 供 scoring/adversarial/promotion 共享
 
 use serde::{Deserialize, Serialize};
 
 use df_core::types::{IdeaId, Priority};
 
-/// 捕获一个新想法的输入
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct CaptureInput {
-    /// 标题
-    pub title: String,
-    /// 详细描述
-    pub description: String,
-    /// 优先级
-    #[serde(default)]
-    pub priority: Priority,
-    /// 标签
-    #[serde(default)]
-    pub tags: Vec<String>,
-    /// 来源（如 "用户输入"、"AI 生成"、"会议记录"）
-    pub source: Option<String>,
-}
-
 /// 想法实体
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Idea {
@@ -60,39 +43,3 @@ pub struct IdeaScores {
     /// 综合评分 (加权平均)
     pub overall: f64,
 }
-
-/// 想法捕获器
-pub struct IdeaCapture;
-
-impl IdeaCapture {
-    /// 捕获一个新想法
-    ///
-    /// TODO: 接入存储层持久化
-    pub fn capture(input: CaptureInput) -> Idea {
-        let now = chrono::Utc::now();
-        Idea {
-            id: df_core::types::new_id(),
-            title: input.title,
-            description: input.description,
-            status: df_core::types::IdeaStatus::Draft,
-            priority: input.priority,
-            scores: None,
-            tags: input.tags,
-            source: input.source,
-            related_ids: Vec::new(),
-            created_at: now,
-            updated_at: now,
-        }
-    }
-
-    /// 快速捕获（仅标题）
-    pub fn quick_capture(title: String) -> Idea {
-        Self::capture(CaptureInput {
-            title,
-            description: String::new(),
-            priority: Priority::default(),
-            tags: Vec::new(),
-            source: None,
-        })
-    }
-}