Add structured logging and centralized error handling

- Initialize slog in the serve command with terminal/file support
- Introduce `AppError` with HTTP status for unified service-layer errors
- Replace ad-hoc `api.Error` calls with `api.RespondError`
- Wrap internal errors with `model.NewInternalError` and add reference
  IDs
- Add `RequestID` middleware and switch router from `gin.Default` to
  `gin.New`

internal/handler/account.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"log/slog"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
@@ -37,7 +38,7 @@ func (h *AccountHandler) ListPasskeys(c *gin.Context) {
 
 	creds, err := h.authService.ListPasskeys(c.Request.Context(), userID)
 	if err != nil {
-		api.Error(c, http.StatusInternalServerError, err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -54,13 +55,14 @@ func (h *AccountHandler) CreatePasskey(c *gin.Context) {
 
 	var req createPasskeyRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
-		api.Error(c, http.StatusBadRequest, "invalid request: "+err.Error())
+		slog.DebugContext(c.Request.Context(), "create passkey bind failed", "error", err)
+		api.Error(c, http.StatusBadRequest, "invalid request body")
 		return
 	}
 
 	pk, err := h.authService.CreatePasskey(c.Request.Context(), userID, req.Label)
 	if err != nil {
-		api.Error(c, http.StatusInternalServerError, err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -78,11 +80,7 @@ func (h *AccountHandler) RevokePasskey(c *gin.Context) {
 	}
 
 	if err := h.authService.RevokePasskey(c.Request.Context(), userID, passkeyID); err != nil {
-		if err == model.ErrForbidden {
-			api.Error(c, http.StatusForbidden, err.Error())
-			return
-		}
-		api.Error(c, http.StatusInternalServerError, err.Error())
+		api.RespondError(c, err)
 		return
 	}