docs: changelog + README updates for batch A (migrations, CI, B14/B15/B17)

docs/CHANGELOG.md

@@ -8,6 +8,25 @@ The format loosely follows Keep a Changelog and can be adapted to the team's hab
 
 ## [Unreleased]
 
+### Changed / 变更
+
+- Add ordered migration system with `schema_migrations` tracking and pg advisory lock for safe multi-replica schema evolution. Existing databases are auto-baselined. To change the schema, add a new `NNNN_description.sql` file under `backend/internal/db/migrations/`; never modify an already-applied file. No down migrations — rollback via backup, fix-forward.
+- 新增有序迁移系统，通过 `schema_migrations` 表和 pg advisory lock 实现安全的多副本 schema 演进，已有数据库自动基线化。修改 schema 时在 `backend/internal/db/migrations/` 下新增 `NNNN_description.sql`，已应用的文件不可修改。不支持 down 迁移——回滚靠备份，fix-forward。
+
+### Fixed / 修复
+
+- Serve goroutine `log.Fatalf` replaced with channel-based shutdown to preserve graceful teardown (B14).
+- 服务 goroutine 中的 `log.Fatalf` 改为 channel 通知方式，确保优雅关停流程不被绕过（B14）。
+- `DATABASE_URL` is now validated at startup (required, parseable); empty `REDIS_URL` logs a clear "redis disabled" message (B15).
+- `DATABASE_URL` 在启动时校验（必填、可解析）；空 `REDIS_URL` 记录明确的 "redis disabled" 日志（B15）。
+- `scripts/smoke.sh` aligned with current API contract, removed ignored `root_path` field (B17).
+- `scripts/smoke.sh` 对齐当前 API 契约，移除被忽略的 `root_path` 字段（B17）。
+
+### Added / 新增
+
+- CI workflow (`.github/workflows/ci.yml`) compatible with both GitHub Actions and Gitea Actions.
+- CI 工作流（`.github/workflows/ci.yml`），兼容 GitHub Actions 和 Gitea Actions。
+
 ### Added / 新增
 
 - API: per-user bookmarks — `GET/POST /api/books/:id/bookmarks` (locator+percent snapshot with optional ≤500-char note; list ordered by percent) and `PATCH/DELETE /api/bookmarks/:id`; not-yours uniformly 404. New `bookmarks` table keyed like progress, cleaned up with the user (no cascade on book delete, same precedent).