feat: add hook system, QR code login, and layered cache

- Implement extensible hook system for content moderation with
  builtin and AI-powered moderation hooks
- Add QR code login feature with SSE for real-time status updates
  and scan/confirm/cancel workflow
- Introduce layered cache with local LRU + Redis backend for
  improved read performance
- Refactor post and comment services to use hook-based moderation
  instead of direct AI service calls
- Add local cache configuration options (size, buckets, ttl)

internal/cache/lru_striped.go

@@ -0,0 +1,167 @@
+package cache
+
+import (
+	"math"
+	"runtime"
+	"time"
+
+	"github.com/cespare/xxhash/v2"
+)
+
+type LRUStriped struct {
+	buckets []*LRU
+	name    string
+}
+
+type LRUStripedOptions struct {
+	Size          int
+	DefaultExpiry time.Duration
+	Name          string
+	Buckets       int
+}
+
+func NewLRUStriped(opts *LRUStripedOptions) *LRUStriped {
+	if opts.Buckets <= 0 {
+		opts.Buckets = runtime.NumCPU()
+	}
+	if opts.Buckets < 4 {
+		opts.Buckets = 4
+	}
+	if opts.Size < opts.Buckets {
+		opts.Size = opts.Buckets * 100
+	}
+
+	opts.Size += int(math.Ceil(float64(opts.Size) * 10.0 / 100.0))
+	bucketSize := (opts.Size / opts.Buckets) + (opts.Size % opts.Buckets)
+
+	buckets := make([]*LRU, opts.Buckets)
+	for i := 0; i < opts.Buckets; i++ {
+		buckets[i] = NewLRU(&LRUOptions{
+			Size:          bucketSize,
+			DefaultExpiry: opts.DefaultExpiry,
+			Name:          opts.Name,
+		})
+	}
+
+	return &LRUStriped{
+		buckets: buckets,
+		name:    opts.Name,
+	}
+}
+
+func (l *LRUStriped) hashKey(key string) uint64 {
+	return xxhash.Sum64String(key)
+}
+
+func (l *LRUStriped) keyBucket(key string) *LRU {
+	return l.buckets[l.hashKey(key)%uint64(len(l.buckets))]
+}
+
+func (l *LRUStriped) Set(key string, value any, ttl time.Duration) {
+	l.keyBucket(key).Set(key, value, ttl)
+}
+
+func (l *LRUStriped) Get(key string) (any, bool) {
+	return l.keyBucket(key).Get(key)
+}
+
+func (l *LRUStriped) Delete(key string) {
+	l.keyBucket(key).Delete(key)
+}
+
+func (l *LRUStriped) DeleteByPrefix(prefix string) {
+	for _, bucket := range l.buckets {
+		bucket.DeleteByPrefix(prefix)
+	}
+}
+
+func (l *LRUStriped) Clear() {
+	for _, bucket := range l.buckets {
+		bucket.Clear()
+	}
+}
+
+func (l *LRUStriped) Exists(key string) bool {
+	return l.keyBucket(key).Exists(key)
+}
+
+func (l *LRUStriped) Increment(key string) int64 {
+	return l.keyBucket(key).Increment(key)
+}
+
+func (l *LRUStriped) IncrementBy(key string, value int64) int64 {
+	return l.keyBucket(key).IncrementBy(key, value)
+}
+
+func (l *LRUStriped) Len() int {
+	var total int
+	for _, bucket := range l.buckets {
+		total += bucket.Len()
+	}
+	return total
+}
+
+func (l *LRUStriped) Name() string {
+	return l.name
+}
+
+func (l *LRUStriped) DeleteMulti(keys []string) error {
+	var err error
+	for _, key := range keys {
+		l.Delete(key)
+	}
+	return err
+}
+
+func (l *LRUStriped) GetMulti(keys []string, values []any) []error {
+	errs := make([]error, len(values))
+	for i, key := range keys {
+		if val, ok := l.Get(key); ok {
+			values[i] = val
+		} else {
+			errs[i] = ErrKeyNotFound
+		}
+	}
+	return errs
+}
+
+func (l *LRUStriped) SetMulti(items map[string]any, ttl time.Duration) error {
+	for key, value := range items {
+		l.Set(key, value, ttl)
+	}
+	return nil
+}
+
+func (l *LRUStriped) Keys() []string {
+	keys := make([]string, 0)
+	for _, bucket := range l.buckets {
+		bucket.lock.RLock()
+		for key, ent := range bucket.items {
+			e := ent.Value.(*lruEntry)
+			if e.generation == bucket.currentGeneration && (e.expires.IsZero() || !time.Now().After(e.expires)) {
+				keys = append(keys, key)
+			}
+		}
+		bucket.lock.RUnlock()
+	}
+	return keys
+}
+
+type LRUStripedInterface interface {
+	Set(key string, value any, ttl time.Duration)
+	Get(key string) (any, bool)
+	Delete(key string)
+	DeleteByPrefix(prefix string)
+	Clear()
+	Exists(key string) bool
+	Increment(key string) int64
+	IncrementBy(key string, value int64) int64
+	Len() int
+	Name() string
+	DeleteMulti(keys []string) error
+	GetMulti(keys []string, values []any) []error
+	SetMulti(items map[string]any, ttl time.Duration) error
+	Keys() []string
+}
+
+var _ LRUStripedInterface = (*LRUStriped)(nil)