refactor: introduce Wire dependency injection and interface-based architecture

- Add Google Wire for compile-time dependency injection
- Replace concrete service types with interfaces across handlers
- Remove global state (DB, cache) in favor of constructor injection
- Split monolithic files into focused modules:
  - config: separate files for each config domain
  - dto: converters split by domain (user, post, message, group)
  - cache: separate metrics.go and redis_cache.go
- Introduce unified apperrors package with string-based error codes
- Add transaction support with context-aware repository methods
- Upgrade golang.org/x/crypto from 0.17.0 to 0.26.0

internal/cache/metrics.go

@@ -0,0 +1,65 @@
+package cache
+
+import "sync/atomic"
+
+// cacheMetrics 缓存指标
+type cacheMetrics struct {
+	hit         atomic.Int64
+	miss        atomic.Int64
+	decodeError atomic.Int64
+	setError    atomic.Int64
+	invalidate  atomic.Int64
+}
+
+// metrics 全局缓存指标实例
+var metrics cacheMetrics
+
+// MetricsSnapshot 指标快照
+type MetricsSnapshot struct {
+	Hit         int64
+	Miss        int64
+	DecodeError int64
+	SetError    int64
+	Invalidate  int64
+}
+
+// GetMetricsSnapshot 获取当前指标快照
+func GetMetricsSnapshot() MetricsSnapshot {
+	return MetricsSnapshot{
+		Hit:         metrics.hit.Load(),
+		Miss:        metrics.miss.Load(),
+		DecodeError: metrics.decodeError.Load(),
+		SetError:    metrics.setError.Load(),
+		Invalidate:  metrics.invalidate.Load(),
+	}
+}
+
+// recordHit 记录缓存命中
+func recordHit() {
+	metrics.hit.Add(1)
+}
+
+// recordMiss 记录缓存未命中
+func recordMiss() {
+	metrics.miss.Add(1)
+}
+
+// recordDecodeError 记录解码错误
+func recordDecodeError() {
+	metrics.decodeError.Add(1)
+}
+
+// recordSetError 记录设置错误
+func recordSetError() {
+	metrics.setError.Add(1)
+}
+
+// recordInvalidate 记录缓存失效
+func recordInvalidate() {
+	metrics.invalidate.Add(1)
+}
+
+// recordInvalidateMultiple 记录多个缓存失效
+func recordInvalidateMultiple(count int64) {
+	metrics.invalidate.Add(count)
+}