perf(db): add indexes for trash and admin post list queries

- idx_posts_deleted_at: 回收站查询 WHERE deleted_at IS NOT NULL ORDER BY deleted_at DESC
- idx_posts_created_at_admin: 管理后台全量列表 WHERE deleted_at IS NULL ORDER BY created_at DESC

migrations/011_perf_indexes.sql

@@ -0,0 +1,13 @@
+-- 性能审计补充索引。
+-- 所有索引均为 CREATE INDEX IF NOT EXISTS，对已有数据库安全幂等。
+
+-- 回收站查询：trash.rs 中大量 WHERE deleted_at IS NOT NULL ... ORDER BY deleted_at DESC。
+-- 配合 list_deleted_posts 的 ORDER BY deleted_at DESC 分页。
+CREATE INDEX IF NOT EXISTS idx_posts_deleted_at
+    ON posts(deleted_at DESC) WHERE deleted_at IS NOT NULL;
+
+-- 管理后台列表 list_posts：WHERE deleted_at IS NULL ORDER BY created_at DESC。
+-- 注意 002_posts.sql 已有 idx_posts_status_published（仅 published 分页），
+-- 这里补充未按 status 过滤的管理后台全量列表路径。
+CREATE INDEX IF NOT EXISTS idx_posts_created_at_admin
+    ON posts(created_at DESC) WHERE deleted_at IS NULL;