feat: 预算版本管理API — 修复前端'加载版本失败'(budgetApi.versions未定义+后端无端点)

- 后端: GET /budget/versions(版本列表) POST /versions/submit /versions/approve /versions/diff
- 前端: budgetApi.versions/versionSubmit/versionApprove/versionDiff
- 数据: budget_plans已有v2.0 active 24条
- 验证: 版本列表200(v2.0 24KPI 预算730万) 版本对比200

backend/app/api/budget.py

@@ -954,3 +954,160 @@ def budget_method_comparison(data: dict):
         "recommended": recommended,
         "recommended_name": "零基预算",
     }
+
+
+# ============ 预算版本管理 API（2026-08-25 补充，修复前端"加载版本失败"） ============
+
+@router.get("/versions")
+def list_budget_versions(
+    year: Optional[int] = Query(None, description="预算年份"),
+    db: Session = Depends(get_db),
+    entity_id: int = Depends(get_entity_id),
+):
+    """预算版本列表 — 按版本聚合统计"""
+    query = db.query(BudgetPlan).filter(BudgetPlan.entity_id == entity_id)
+    if year:
+        query = query.filter(BudgetPlan.budget_year == year)
+
+    rows = query.all()
+    # 按version+status聚合
+    version_map = {}
+    for r in rows:
+        key = (r.version or "v1.0", r.status or "active")
+        if key not in version_map:
+            version_map[key] = {
+                "version": r.version or "v1.0",
+                "status": r.status or "active",
+                "kpi_count": 0,
+                "total_budget": 0.0,
+                "periods": set(),
+                "updated_at": r.updated_at,
+            }
+        v = version_map[key]
+        v["kpi_count"] += 1
+        v["total_budget"] += r.budget_value or 0
+        v["periods"].add(r.period)
+        if r.updated_at and (v["updated_at"] is None or r.updated_at > v["updated_at"]):
+            v["updated_at"] = r.updated_at
+
+    result = []
+    for key, v in version_map.items():
+        result.append({
+            "version": v["version"],
+            "status": v["status"],
+            "kpi_count": v["kpi_count"],
+            "total_budget": round(v["total_budget"], 2),
+            "period_count": len(v["periods"]),
+            "year": year,
+            "updated_at": v["updated_at"].strftime("%Y-%m-%d %H:%M") if v["updated_at"] else "",
+        })
+    result.sort(key=lambda x: x["version"], reverse=True)
+    return result
+
+
+@router.post("/versions/submit")
+def submit_budget_version(
+    data: dict,
+    db: Session = Depends(get_db),
+    entity_id: int = Depends(get_entity_id),
+):
+    """提交版本审批：active → submitted"""
+    version = data.get("version", "v1.0")
+    rows = db.query(BudgetPlan).filter(
+        BudgetPlan.entity_id == entity_id,
+        BudgetPlan.version == version,
+    ).all()
+    if not rows:
+        raise HTTPException(404, f"版本 {version} 不存在")
+    for r in rows:
+        r.status = "submitted"
+    db.commit()
+    return {"success": True, "version": version, "status": "submitted", "count": len(rows)}
+
+
+@router.post("/versions/approve")
+def approve_budget_version(
+    data: dict,
+    db: Session = Depends(get_db),
+    entity_id: int = Depends(get_entity_id),
+):
+    """审批版本：submitted → approved/rejected"""
+    version = data.get("version", "v1.0")
+    action = data.get("action", "approved")
+    rows = db.query(BudgetPlan).filter(
+        BudgetPlan.entity_id == entity_id,
+        BudgetPlan.version == version,
+    ).all()
+    if not rows:
+        raise HTTPException(404, f"版本 {version} 不存在")
+    new_status = "approved" if action == "approved" else "rejected"
+    for r in rows:
+        r.status = new_status
+    db.commit()
+    return {"success": True, "version": version, "status": new_status, "count": len(rows)}
+
+
+@router.post("/versions/diff")
+def diff_budget_versions(
+    data: dict,
+    db: Session = Depends(get_db),
+    entity_id: int = Depends(get_entity_id),
+):
+    """版本差异对比：v1.0 vs v2.0 逐KPI差异"""
+    version_a = data.get("version_a", "")
+    version_b = data.get("version_b", "")
+    year = data.get("year")
+    if not version_a or not version_b:
+        raise HTTPException(400, "需要 version_a 和 version_b")
+
+    def load_version(ver: str):
+        query = db.query(BudgetPlan).filter(
+            BudgetPlan.entity_id == entity_id,
+            BudgetPlan.version == ver,
+        )
+        if year:
+            query = query.filter(BudgetPlan.budget_year == year)
+        return {r.kpi_id: r for r in query.all()}
+
+    va = load_version(version_a)
+    vb = load_version(version_b)
+
+    kpi_ids = set(va.keys()) | set(vb.keys())
+    kpis = db.query(KPIDefinition).filter(KPIDefinition.id.in_(kpi_ids)).all()
+    kpi_map = {k.id: k for k in kpis}
+
+    diffs = []
+    total_a = total_b = 0.0
+    changed_count = 0
+    for kid in sorted(kpi_ids):
+        ra = va.get(kid)
+        rb = vb.get(kid)
+        val_a = ra.budget_value if ra else 0
+        val_b = rb.budget_value if rb else 0
+        total_a += val_a
+        total_b += val_b
+        k = kpi_map.get(kid)
+        diff = val_b - val_a
+        if abs(diff) > 0.001:
+            changed_count += 1
+        diffs.append({
+            "kpi_code": k.kpi_code if k else "",
+            "kpi_name": k.kpi_name if k else f"KPI-{kid}",
+            "version_a": round(val_a, 2),
+            "version_b": round(val_b, 2),
+            "diff": round(diff, 2),
+        })
+
+    diffs.sort(key=lambda x: -abs(x["diff"]))
+    return {
+        "summary": {
+            "version_a": version_a,
+            "version_b": version_b,
+            "kpi_total": len(kpi_ids),
+            "changed_count": changed_count,
+            "total_a": round(total_a, 2),
+            "total_b": round(total_b, 2),
+            "total_diff": round(total_b - total_a, 2),
+        },
+        "diffs": diffs,
+    }