refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

pkg/persistence/batchwriter/config.go

@@ -0,0 +1,69 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package batchwriter
+
+import (
+	"fmt"
+	"time"
+)
+
+const (
+	defaultQueueSize    = 10_000
+	defaultMaxBatchSize = 1_000
+	defaultMinBatchSize = 50
+	defaultFlushEvery   = time.Second
+)
+
+// Config controls queue capacity and flush thresholds for a Writer instance.
+type Config struct {
+	// Name identifies the writer in logs and diagnostics. Optional.
+	Name string
+
+	// QueueSize is the buffered channel capacity.
+	QueueSize int
+
+	// MaxBatchSize triggers a flush when the in-memory batch reaches this count.
+	MaxBatchSize int
+
+	// MinBatchSize is the minimum in-memory batch size for time-based flushes.
+	// Zero disables the threshold and preserves legacy interval flush behavior.
+	// When set, interval flushes below this size are skipped unless MaxFlushWait elapses.
+	MinBatchSize int
+
+	// FlushInterval is how often the worker checks whether a time-based flush should run.
+	FlushInterval time.Duration
+
+	// MaxFlushWait forces a flush of any non-empty batch once the oldest item has waited
+	// this long, even if MinBatchSize has not been reached. Zero disables the force path.
+	MaxFlushWait time.Duration
+}
+
+// DefaultConfig returns production-friendly defaults aligned with audit log batching.
+func DefaultConfig() Config {
+	return Config{
+		QueueSize:     defaultQueueSize,
+		MaxBatchSize:  defaultMaxBatchSize,
+		MinBatchSize:  defaultMinBatchSize,
+		FlushInterval: defaultFlushEvery,
+	}
+}
+
+func (c Config) validate() error {
+	if c.QueueSize <= 0 {
+		return fmt.Errorf("batchwriter: queue size must be positive")
+	}
+	if c.MaxBatchSize <= 0 {
+		return fmt.Errorf("batchwriter: max batch size must be positive")
+	}
+	if c.MinBatchSize < 0 {
+		return fmt.Errorf("batchwriter: min batch size must be non-negative")
+	}
+	if c.FlushInterval <= 0 {
+		return fmt.Errorf("batchwriter: flush interval must be positive")
+	}
+	if c.MaxFlushWait < 0 {
+		return fmt.Errorf("batchwriter: max flush wait must be non-negative")
+	}
+	return nil
+}