Add read-only sharing, API tokens and OpenAPI spec

- Share a note as a live read-only page at /s/{token} with optional password and expiry
- Share page renders with the shared parser (TOC, footnotes, math, Mermaid, code highlighting)
  and only serves images from the note's own .assets directory
- Shares follow renames made through the API or externally
- Manage shares and API tokens from the command palette and file tree
- Accept read/write API tokens as Bearer credentials; management endpoints require a session
- Serve a hand-written openapi.json, checked against the route table in tests

internal/auth/auth.go

@@ -1,7 +1,8 @@
-// Package auth 实现单用户登录：Argon2id 密码哈希、会话令牌与登录限速。
+// Package auth 实现单用户登录（Argon2id 密码哈希、会话令牌、登录限速），以及分享密码与 API 令牌的校验。
 package auth
 
 import (
+	"crypto/hmac"
 	"crypto/rand"
 	"crypto/sha256"
 	"crypto/subtle"
@@ -20,6 +21,8 @@ import (
 
 const (
 	passwordKey    = "auth.password"
+	shareSecretKey = "share.secret"
+	apiTokenPrefix = "rm_"
 	SessionTTL     = 30 * 24 * time.Hour
 	MinPasswordLen = 8
 
@@ -39,6 +42,7 @@ var (
 	ErrWeakPassword   = fmt.Errorf("密码至少 %d 位", MinPasswordLen)
 	ErrBadCredentials = errors.New("密码错误")
 	ErrRateLimited    = errors.New("尝试次数过多，请稍后再试")
+	ErrBadScope       = errors.New("权限范围只能是 read 或 write")
 )
 
 type Manager struct {
@@ -135,6 +139,92 @@ func (m *Manager) Validate(token string) (bool, error) {
 
 func (m *Manager) Logout(token string) error { return m.store.DeleteSession(hashToken(token)) }
 
+// ---- 分享 ----
+
+// HashSharePassword 为分享密码生成哈希；空密码表示不设密码，返回空字符串
+func HashSharePassword(password string) string {
+	if password == "" {
+		return ""
+	}
+	return hashPassword(password)
+}
+
+// CheckSharePassword 校验分享密码，与登录共用按来源的失败限速
+func (m *Manager) CheckSharePassword(ip, hash, password string) error {
+	if !m.allow(ip) {
+		return ErrRateLimited
+	}
+	ok, err := verifyPassword(hash, password)
+	if err != nil {
+		return err
+	}
+	if !ok {
+		m.recordFailure(ip)
+		return ErrBadCredentials
+	}
+	return nil
+}
+
+// ShareCookie 生成输入分享密码后发给访客的凭据：绑定分享令牌与密码哈希，撤销分享即失效
+func (m *Manager) ShareCookie(token, passwordHash string) (string, error) {
+	secret, err := m.shareSecret()
+	if err != nil {
+		return "", err
+	}
+	mac := hmac.New(sha256.New, secret)
+	mac.Write([]byte(token + "\x00" + passwordHash))
+	return base64.RawURLEncoding.EncodeToString(mac.Sum(nil)), nil
+}
+
+func (m *Manager) ValidShareCookie(cookie, token, passwordHash string) (bool, error) {
+	want, err := m.ShareCookie(token, passwordHash)
+	if err != nil {
+		return false, err
+	}
+	return hmac.Equal([]byte(cookie), []byte(want)), nil
+}
+
+// shareSecret 读取签名密钥，首次使用时生成并保存
+func (m *Manager) shareSecret() ([]byte, error) {
+	v, ok, err := m.store.Setting(shareSecretKey)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		if _, err := m.store.SetSettingIfAbsent(shareSecretKey, randomToken()); err != nil {
+			return nil, err
+		}
+		// 并发首次生成时以先写入的为准
+		if v, _, err = m.store.Setting(shareSecretKey); err != nil {
+			return nil, err
+		}
+	}
+	return base64.RawURLEncoding.DecodeString(v)
+}
+
+// ---- API 令牌 ----
+
+// CreateAPIToken 创建令牌，返回只显示这一次的明文
+func (m *Manager) CreateAPIToken(name, scope string) (string, store.APIToken, error) {
+	if scope != "read" && scope != "write" {
+		return "", store.APIToken{}, ErrBadScope
+	}
+	plain := apiTokenPrefix + randomToken()
+	t := store.APIToken{ID: randomCode(), Name: name, Hash: hashToken(plain), Scope: scope, CreatedAt: time.Now().UnixMilli()}
+	if err := m.store.CreateAPIToken(t); err != nil {
+		return "", store.APIToken{}, err
+	}
+	return plain, t, nil
+}
+
+// ValidateAPIToken 返回令牌的权限范围；无效时 ok 为 false
+func (m *Manager) ValidateAPIToken(plain string) (scope string, ok bool, err error) {
+	if !strings.HasPrefix(plain, apiTokenPrefix) {
+		return "", false, nil
+	}
+	return m.store.UseAPIToken(hashToken(plain), time.Now().UnixMilli())
+}
+
 // ---- 限速：同一来源在时间窗口内失败过多则拒绝 ----
 
 func (m *Manager) allow(ip string) bool {
@@ -204,6 +294,13 @@ func randomToken() string {
 	return base64.RawURLEncoding.EncodeToString(b)
 }
 
+// NewShareToken 生成分享链接中的令牌（128 位随机数，比会话令牌短，便于复制）
+func NewShareToken() string {
+	b := make([]byte, 16)
+	rand.Read(b)
+	return base64.RawURLEncoding.EncodeToString(b)
+}
+
 func hashToken(token string) string {
 	sum := sha256.Sum256([]byte(token))
 	return hex.EncodeToString(sum[:])