feat(linkage): 计划-鞍座-实绩-停机联动 + 成本管理页

后端：
- 计划录入即「准备好」，队首(最早)自动「在线」(唯一)
- 新增上卷鞍座联动引擎 line_service：移动→鞍座→(有速度/投入生产)→生产中
  →带头达2000m→生产完成并自动产生实绩、持久化运行数据
- 停机自动检测：线速度为0持续>10min 自动新增待补充停机记录，恢复后自动结束
- /plan/start=移动到鞍座, 新增 /plan/{id}/commit 投入生产, /plan/saddle/current,
  /plan/seed 批量插入(轧制力模式)；后台引擎循环自动推进
- 新增成本管理：CostRecord 模型 + /cost CRUD + 9 类成本项(乳化液/盐酸/碱/电/水/蒸汽…)

前端：
- 入口跟踪重构为单个上卷鞍座工位(实时速度/带头长度进度/投入生产)+待上卷卡片+队列，
  计划列表/卡片/队列均可「移动」
- 新增成本管理页(成本项切换 + 柱+线图 + 明细表 + 时间筛选 + 新增)，布局参考乳化液耗量统计

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/api/cost.py

@@ -0,0 +1,112 @@
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, asc
+from typing import Optional
+from datetime import datetime
+
+from app.database import get_db
+from app.models.cost import CostRecord
+from app.schemas.cost import CostItem, CostCreate, CostUpdate, CostOut
+from app.schemas.common import Response
+from app.services.auth_service import get_current_user
+
+router = APIRouter()
+
+# 预定义成本/消耗项
+COST_ITEMS = [
+    {"item": "emulsion",    "item_name": "乳化液",   "unit": "L",   "unit_cost_label": "L/t"},
+    {"item": "acid",        "item_name": "盐酸",     "unit": "L",   "unit_cost_label": "L/t"},
+    {"item": "alkali",      "item_name": "脱脂碱液", "unit": "kg",  "unit_cost_label": "kg/t"},
+    {"item": "power",       "item_name": "电耗",     "unit": "kWh", "unit_cost_label": "kWh/t"},
+    {"item": "water",       "item_name": "新水",     "unit": "m³",  "unit_cost_label": "m³/t"},
+    {"item": "steam",       "item_name": "蒸汽",     "unit": "t",   "unit_cost_label": "kg/t"},
+    {"item": "antirust_oil","item_name": "防锈油",   "unit": "L",   "unit_cost_label": "L/t"},
+    {"item": "inhibitor",   "item_name": "缓蚀剂",   "unit": "kg",  "unit_cost_label": "g/t"},
+    {"item": "roll",        "item_name": "辊耗",     "unit": "支",  "unit_cost_label": "支/kt"},
+]
+_ITEM_MAP = {x["item"]: x for x in COST_ITEMS}
+
+
+def _parse_dt(s):
+    if not s:
+        return None
+    try:
+        return datetime.fromisoformat(s.replace('Z', ''))
+    except Exception:
+        return None
+
+
+@router.get("/items", response_model=Response[list[CostItem]])
+async def list_items(_ = Depends(get_current_user)):
+    return Response.ok([CostItem(**x) for x in COST_ITEMS])
+
+
+@router.get("/", response_model=Response[list[CostOut]])
+async def list_records(
+    item: Optional[str] = None,
+    start_date: Optional[str] = Query(None),
+    end_date: Optional[str] = Query(None),
+    db: AsyncSession = Depends(get_db),
+    _ = Depends(get_current_user),
+):
+    query = select(CostRecord).order_by(asc(CostRecord.record_date))
+    if item:
+        query = query.where(CostRecord.item == item)
+    _sd = _parse_dt(start_date)
+    if _sd:
+        query = query.where(CostRecord.record_date >= _sd)
+    _ed = _parse_dt(end_date)
+    if _ed:
+        query = query.where(CostRecord.record_date <= _ed)
+    result = await db.execute(query)
+    return Response.ok([CostOut.model_validate(r) for r in result.scalars()])
+
+
+@router.post("/", response_model=Response[CostOut])
+async def create_record(
+    body: CostCreate,
+    db: AsyncSession = Depends(get_db),
+    current_user = Depends(get_current_user),
+):
+    meta = _ITEM_MAP.get(body.item)
+    if not meta:
+        raise HTTPException(status_code=400, detail="未知成本项")
+    rec = CostRecord(
+        item=body.item,
+        item_name=meta["item_name"],
+        unit=meta["unit"],
+        record_date=body.record_date,
+        shift_a=body.shift_a or 0,
+        shift_b=body.shift_b or 0,
+        unit_cost=body.unit_cost or 0,
+        remark=body.remark,
+        created_by=current_user.username,
+    )
+    db.add(rec)
+    await db.flush()
+    return Response.ok(CostOut.model_validate(rec))
+
+
+@router.put("/{rec_id}", response_model=Response[CostOut])
+async def update_record(
+    rec_id: int,
+    body: CostUpdate,
+    db: AsyncSession = Depends(get_db),
+    _ = Depends(get_current_user),
+):
+    rec = await db.get(CostRecord, rec_id)
+    if not rec:
+        raise HTTPException(status_code=404, detail="记录不存在")
+    for k, v in body.model_dump(exclude_none=True).items():
+        setattr(rec, k, v)
+    await db.flush()
+    return Response.ok(CostOut.model_validate(rec))
+
+
+@router.delete("/{rec_id}", response_model=Response[dict])
+async def delete_record(rec_id: int, db: AsyncSession = Depends(get_db), _ = Depends(get_current_user)):
+    rec = await db.get(CostRecord, rec_id)
+    if not rec:
+        raise HTTPException(status_code=404, detail="记录不存在")
+    await db.delete(rec)
+    return Response.ok({"deleted": rec_id})