fix(finance): 收敛内部 SKU 履约路由与载体状态

统一内部 SKU 与渠道主/兜底解析，禁止并列主渠道。

运营指定渠道改为先创建真实载体，失败保持明确 pending。

历史缺载体、多载体冲突和自动发货兜底统一由管道修复。

迁移人工配置与旧 sku_code 规则，补充严格预检和集成测试。

apps/backend/scripts/cleanup-legacy-sku-code-rules.ts

@@ -88,6 +88,17 @@ async function main() {
       `,
       [internalSku, rule.channel, rule.priority, rule.source || 'operator'],
     )
+    await query(
+      `UPDATE internal_sku_channels
+       SET is_fallback = TRUE,
+           priority = GREATEST(priority, 90),
+           updated_at = NOW()
+       WHERE btrim(internal_sku) = $1
+         AND channel <> $2
+         AND enabled = TRUE
+         AND is_fallback = FALSE`,
+      [internalSku, rule.channel],
+    )
     await query(
       `
         INSERT INTO internal_sku_channels (
@@ -95,6 +106,7 @@ async function main() {
         ) VALUES ($1, $2, $3, FALSE, TRUE, 'legacy-rule')
         ON CONFLICT (internal_sku, channel) DO UPDATE SET
           priority = LEAST(internal_sku_channels.priority, EXCLUDED.priority),
+          is_fallback = FALSE,
           enabled = TRUE,
           updated_at = NOW()
       `,