fix(cluster-2): error contract unification (C1/M10/M11/M12)

- http: handleError now recognizes domain.ErrNotFound in addition to the
  common errors.ErrNotFound sentinel, so repo-not-found maps to 404
  instead of 500 (the two packages use distinct error types)
- sqlite_course_repository: propagate listCount errors instead of logging
  and swallowing them, which left callers with a silent Count=0
- synchandler: collect course/organization insert failures into a
  function-scoped error via errors.Join and return it; previously the
  loop-local err was overwritten and the handler always returned nil,
  hiding all insert failures

internal/kurious/adapters/sqlite_course_repository.go

@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"git.loyso.art/frx/kurious/internal/common/nullable"
-	"git.loyso.art/frx/kurious/internal/common/xcontext"
 	"git.loyso.art/frx/kurious/internal/common/xslices"
 	"git.loyso.art/frx/kurious/internal/kurious/domain"
 
@@ -112,7 +111,7 @@ func (r *sqliteCourseRepository) List(
 
 	result.Count, err = r.listCount(ctx, params)
 	if err != nil {
-		xcontext.LogWithWarnError(ctx, r.log, err, "unable to list count")
+		return result, fmt.Errorf("listing count: %w", err)
 	}
 
 	span.SetAttributes(

internal/kurious/ports/background/synchandler.go

@@ -85,6 +85,7 @@ func (h *syncSravniHandler) Handle(ctx context.Context) (err error) {
 	courses := make([]sravni.Course, 0, 1024)
 	buffer := make([]sravni.Course, 0, 512)
 	organizations := make([]sravni.Organization, 0, 256)
+	var insertErr error
 	for _, learningType := range learningTypes.Fields {
 		select {
 		case <-ctx.Done():
@@ -174,22 +175,22 @@ func (h *syncSravniHandler) Handle(ctx context.Context) (err error) {
 
 		var insertCourseSuccess bool
 		if len(courses) > 0 {
-			err = h.insertCourses(lctx, courses)
-			if err != nil {
-				xcontext.LogWithError(lctx, h.log, err, "unable to insert courses")
+			if cerr := h.insertCourses(lctx, courses); cerr != nil {
+				xcontext.LogWithError(lctx, h.log, cerr, "unable to insert courses")
+				insertErr = errors.Join(insertErr, cerr)
+			} else {
+				insertCourseSuccess = true
 			}
-
-			insertCourseSuccess = err == nil
 		}
 
 		var insertOrgsSuccess bool
 		if len(organizations) > 0 {
-			err = h.insertOrganizations(lctx, organizations)
-			if err != nil {
-				xcontext.LogWithError(lctx, h.log, err, "unable to insert courses")
+			if oerr := h.insertOrganizations(lctx, organizations); oerr != nil {
+				xcontext.LogWithError(lctx, h.log, oerr, "unable to insert organizations")
+				insertErr = errors.Join(insertErr, oerr)
+			} else {
+				insertOrgsSuccess = true
 			}
-
-			insertOrgsSuccess = err == nil
 		}
 
 		elapsed = time.Since(start) - elapsed
@@ -205,7 +206,7 @@ func (h *syncSravniHandler) Handle(ctx context.Context) (err error) {
 		)
 	}
 
-	return nil
+	return insertErr
 }
 
 func (h *syncSravniHandler) loadEducationalProducts(ctx context.Context, learningType, courseThematic string, buf []sravni.Course) ([]sravni.Course, map[string]sravni.Organization, error) {

internal/kurious/ports/http/server.go

@@ -9,6 +9,7 @@ import (
 
 	"git.loyso.art/frx/kurious/internal/common/errors"
 	"git.loyso.art/frx/kurious/internal/common/xcontext"
+	"git.loyso.art/frx/kurious/internal/kurious/domain"
 	"git.loyso.art/frx/kurious/internal/kurious/service"
 	"git.loyso.art/frx/kurious/pkg/xdefault"
 
@@ -49,7 +50,7 @@ func handleError(ctx context.Context, err error, w http.ResponseWriter, log *slo
 	case stderrors.As(err, &valErr):
 		errorString = valErr.Error()
 		code = http.StatusBadRequest
-	case stderrors.Is(err, errors.ErrNotFound):
+	case stderrors.Is(err, errors.ErrNotFound), stderrors.Is(err, domain.ErrNotFound):
 		errorString = err.Error()
 		code = http.StatusNotFound
 	default: