feat(server): add Go backend with vault, auth, events and REST API

- vault: path validation (no traversal, hidden segments or symlink
  escape), atomic writes with If-Match/If-None-Match revisions, moves
  that carry the note's .assets folder and rewrite its image links,
  trash with restore, content-addressed asset uploads
- auth: single-user Argon2id password, sliding sessions in SQLite,
  login rate limiting, first-run setup gated by a one-time code written
  to the data directory
- watch: fsnotify plus periodic rescans diffed against a snapshot, so
  both RawMark and external edits are broadcast as tree/changed/moved/
  deleted events over WebSocket
- api: stdlib router, SameSite=Strict cookies plus Origin checks,
  sandboxed raw file serving, embedded SPA with gzip and CSP

internal/auth/auth.go

@@ -0,0 +1,225 @@
+// 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
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/crypto/argon2"
+
+	"rawmark/internal/store"
+)
+
+const (
+	passwordKey    = "auth.password"
+	SessionTTL     = 30 * 24 * time.Hour
+	MinPasswordLen = 8
+
+	// RFC 9106 推荐的第二组参数（内存受限环境）
+	argonTime    = 3
+	argonMemory  = 64 * 1024
+	argonThreads = 4
+	argonKeyLen  = 32
+
+	maxFailures   = 5
+	failureWindow = 15 * time.Minute
+)
+
+var (
+	ErrAlreadySetUp   = errors.New("已完成初始化")
+	ErrBadSetupCode   = errors.New("启动码错误")
+	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")
+)
+
+type Manager struct {
+	store *store.Store
+	// 首次初始化需要的一次性启动码，仅打印在服务日志中，防止部署后被他人抢先设置密码
+	setupCode string
+
+	mu       sync.Mutex
+	failures map[string][]time.Time
+}
+
+func New(s *store.Store) (*Manager, error) {
+	m := &Manager{store: s, failures: map[string][]time.Time{}}
+	ok, err := m.IsSetUp()
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		m.setupCode = randomCode()
+	}
+	return m, nil
+}
+
+// SetupCode 返回启动码；已初始化时为空
+func (m *Manager) SetupCode() string {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return m.setupCode
+}
+
+func (m *Manager) IsSetUp() (bool, error) {
+	_, ok, err := m.store.Setting(passwordKey)
+	return ok, err
+}
+
+func (m *Manager) Setup(code, password string) error {
+	expected := m.SetupCode()
+	if expected == "" {
+		return ErrAlreadySetUp
+	}
+	if subtle.ConstantTimeCompare([]byte(strings.ToUpper(strings.TrimSpace(code))), []byte(expected)) != 1 {
+		return ErrBadSetupCode
+	}
+	if len([]rune(password)) < MinPasswordLen {
+		return ErrWeakPassword
+	}
+	ok, err := m.store.SetSettingIfAbsent(passwordKey, hashPassword(password))
+	if err != nil {
+		return err
+	}
+	if !ok {
+		return ErrAlreadySetUp
+	}
+	m.mu.Lock()
+	m.setupCode = ""
+	m.mu.Unlock()
+	return nil
+}
+
+// Login 校验密码并创建会话，返回明文令牌（仅存哈希）
+func (m *Manager) Login(ip, password string) (string, error) {
+	if !m.allow(ip) {
+		return "", ErrRateLimited
+	}
+	encoded, ok, err := m.store.Setting(passwordKey)
+	if err != nil {
+		return "", err
+	}
+	if !ok {
+		return "", ErrBadCredentials
+	}
+	valid, err := verifyPassword(encoded, password)
+	if err != nil {
+		return "", err
+	}
+	if !valid {
+		m.recordFailure(ip)
+		return "", ErrBadCredentials
+	}
+	m.clearFailures(ip)
+	token := randomToken()
+	if err := m.store.CreateSession(hashToken(token), time.Now().Add(SessionTTL)); err != nil {
+		return "", err
+	}
+	return token, nil
+}
+
+func (m *Manager) Validate(token string) (bool, error) {
+	if token == "" {
+		return false, nil
+	}
+	return m.store.SessionValid(hashToken(token), time.Now().Add(SessionTTL))
+}
+
+func (m *Manager) Logout(token string) error { return m.store.DeleteSession(hashToken(token)) }
+
+// ---- 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 {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	cutoff := time.Now().Add(-failureWindow)
+	recent := m.failures[ip][:0]
+	for _, t := range m.failures[ip] {
+		if t.After(cutoff) {
+			recent = append(recent, t)
+		}
+	}
+	m.failures[ip] = recent
+	return len(recent) < maxFailures
+}
+
+func (m *Manager) recordFailure(ip string) {
+	m.mu.Lock()
+	m.failures[ip] = append(m.failures[ip], time.Now())
+	m.mu.Unlock()
+}
+
+func (m *Manager) clearFailures(ip string) {
+	m.mu.Lock()
+	delete(m.failures, ip)
+	m.mu.Unlock()
+}
+
+// ---- 密码与令牌 ----
+
+func hashPassword(password string) string {
+	salt := make([]byte, 16)
+	rand.Read(salt)
+	key := argon2.IDKey([]byte(password), salt, argonTime, argonMemory, argonThreads, argonKeyLen)
+	b64 := base64.RawStdEncoding
+	return fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s", argon2.Version, argonMemory, argonTime, argonThreads,
+		b64.EncodeToString(salt), b64.EncodeToString(key))
+}
+
+func verifyPassword(encoded, password string) (bool, error) {
+	parts := strings.Split(encoded, "$")
+	if len(parts) != 6 || parts[1] != "argon2id" {
+		return false, errors.New("密码哈希格式无法识别")
+	}
+	var mem uint32
+	var t uint32
+	var p uint8
+	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &mem, &t, &p); err != nil {
+		return false, fmt.Errorf("密码哈希参数无法解析: %w", err)
+	}
+	b64 := base64.RawStdEncoding
+	salt, err := b64.DecodeString(parts[4])
+	if err != nil {
+		return false, err
+	}
+	want, err := b64.DecodeString(parts[5])
+	if err != nil {
+		return false, err
+	}
+	got := argon2.IDKey([]byte(password), salt, t, mem, p, uint32(len(want)))
+	return subtle.ConstantTimeCompare(got, want) == 1, nil
+}
+
+func randomToken() string {
+	b := make([]byte, 32)
+	rand.Read(b)
+	return base64.RawURLEncoding.EncodeToString(b)
+}
+
+func hashToken(token string) string {
+	sum := sha256.Sum256([]byte(token))
+	return hex.EncodeToString(sum[:])
+}
+
+// randomCode 生成形如 ABCD-EFGH 的启动码，去掉易混淆字符
+func randomCode() string {
+	const alphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
+	b := make([]byte, 8)
+	rand.Read(b)
+	out := make([]byte, 0, 9)
+	for i, c := range b {
+		if i == 4 {
+			out = append(out, '-')
+		}
+		out = append(out, alphabet[int(c)%len(alphabet)])
+	}
+	return string(out)
+}