docs(comments): 注释中文化 · internal/runtime/memory（31 文件，纯替换）

- 只翻注释/文档字符串：820 增 / 820 删 严格 1:1；剥掉整行注释与行尾注释尾巴后，
  逐文件与 HEAD 比对「代码部分差异 = 0」；裁决/design 编号计数逐项与 HEAD 一致
- 保留可执行 SQL 样例、SQLite 报错原文、pgvector/HNSW/ANN/BLOB 等技术词原文
- 复核：go build 绿 + memory/projectindex/vector 三包测试绿；gofmt 仅剩 2 个既有未格式化文件（改动前即如此，未顺手修）

internal/runtime/memory/projectindex/project.go

@@ -11,10 +11,10 @@ import (
 	"time"
 )
 
-// Project is a project index entry (design §3): the project marker that links
-// its chapters, together with the project's description. It is layer 1 (index
-// entry) and layer 2 (description) of the hierarchy. The zero value is not a
-// valid project: ID and Title are required.
+// Project 是一个项目索引条目（design §3）：链接其
+// 各章节的项目标示，连同项目描述。它是层级的第 1 层（索引
+// 条目）与第 2 层（描述）。零值不是
+// 合法项目：ID 与 Title 必填。
 type Project struct {
 	ID        string
 	Title     string
@@ -23,10 +23,10 @@ type Project struct {
 	UpdatedAt time.Time
 }
 
-// PutProject upserts p by id. On an existing id it updates title, desc, and
-// updated_at while preserving the original created_at; on a new id it assigns
-// missing timestamps and inserts. A blank id or title returns ErrMissingProject
-// or ErrMissingTitle.
+// PutProject 按 id upsert p。id 已存在时更新 title、desc 与
+// updated_at，并保留原始的 created_at；id 为新值时
+// 补齐缺失时间戳并插入。id 或 title 为空返回 ErrMissingProject
+// 或 ErrMissingTitle。
 func (s *Store) PutProject(ctx context.Context, p Project) error {
 	if strings.TrimSpace(p.ID) == "" {
 		return ErrMissingProject
@@ -55,8 +55,8 @@ func (s *Store) PutProject(ctx context.Context, p Project) error {
 	return nil
 }
 
-// GetProject returns the project with the given id. It returns ErrProjectNotFound
-// when the id is blank or does not exist.
+// GetProject 返回给定 id 的项目。id 为空或
+// 不存在时返回 ErrProjectNotFound。
 func (s *Store) GetProject(ctx context.Context, id string) (*Project, error) {
 	if strings.TrimSpace(id) == "" {
 		return nil, ErrProjectNotFound
@@ -73,10 +73,10 @@ func (s *Store) GetProject(ctx context.Context, id string) (*Project, error) {
 	return p, nil
 }
 
-// DeleteProject removes the project by id and, as a cascade, every chapter that
-// references it. It returns ErrProjectNotFound when the id is blank or no
-// project row was removed. The project removal and the chapter removal happen in
-// one transaction so a failure never leaves an orphaned project or chapter.
+// DeleteProject 按 id 删除项目，并级联删除引用它的每个
+// 章节。id 为空、或没有删除任何
+// 项目行时返回 ErrProjectNotFound。删项目与删章节发生在
+// 同一事务内，因此失败绝不会留下孤儿项目或章节。
 func (s *Store) DeleteProject(ctx context.Context, id string) error {
 	if strings.TrimSpace(id) == "" {
 		return ErrProjectNotFound
@@ -113,7 +113,7 @@ func (s *Store) DeleteProject(ctx context.Context, id string) error {
 	return nil
 }
 
-// scanProject reads one project row.
+// scanProject 读取一行 project。
 func scanProject(sc rowScanner) (*Project, error) {
 	var (
 		p                   Project
@@ -132,9 +132,9 @@ func scanProject(sc rowScanner) (*Project, error) {
 	return &p, nil
 }
 
-// newID returns a 128-bit cryptographically random id, hex-encoded. It avoids a
-// UUID dependency so the package stays self-contained. rand.Read fails only if
-// the platform entropy source is broken, so the error is propagated.
+// newID 返回一个 128 位密码学随机 id，十六进制编码。它避开
+// UUID 依赖，使本包保持自包含。rand.Read 只在
+// 平台熵源损坏时失败，因此错误向上传播。
 func newID() (string, error) {
 	b := make([]byte, 16)
 	if _, err := rand.Read(b); err != nil {