refactor(api): unify error handling and split upload/oauth god modules

Replace c.JSON(200, response.Err) and middleware gin.H bypasses with
response.Abort* helpers so errors flow through Gin Error chain and
ErrorHandlerMiddleware for OTel trace correlation.

Split oauth/sources.go into domain-focused files and decompose upload
into handler/filesrv/stats/task/cache/storage/util subpackages with a
root facade preserving existing import paths.

internal/apps/upload/cache/access_cache.go

@@ -0,0 +1,142 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package cache provides in-process upload access-control caches.
+package cache
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/Rain-kl/Wavelet/internal/apps/upload/shared"
+	uploadstorage "github.com/Rain-kl/Wavelet/internal/apps/upload/storage"
+	"github.com/Rain-kl/Wavelet/internal/db"
+	"github.com/Rain-kl/Wavelet/internal/model"
+	"github.com/Rain-kl/Wavelet/internal/storage"
+)
+
+const fileAccessInvalidationChannel = "upload:file_access_invalidation"
+
+var (
+	accessCacheOnce sync.Once
+
+	fileAccessWhitelistMu        sync.RWMutex
+	fileAccessWhitelistTypes     map[string]struct{}
+	fileAccessWhitelistValid     bool
+	fileAccessWhitelistCheckedAt time.Time
+)
+
+// ResetAccessCaches clears in-process upload access caches.
+func ResetAccessCaches() {
+	uploadstorage.ResetMigrationAccessCache()
+
+	fileAccessWhitelistMu.Lock()
+	fileAccessWhitelistValid = false
+	fileAccessWhitelistTypes = nil
+	fileAccessWhitelistMu.Unlock()
+}
+
+// PublishAccessCacheInvalidation broadcasts upload access cache eviction to all nodes.
+func PublishAccessCacheInvalidation(ctx context.Context) {
+	if db.Redis != nil {
+		_ = db.Redis.Publish(ctx, fileAccessInvalidationChannel, "reset").Err()
+	}
+}
+
+func ensureAccessCacheListener() {
+	accessCacheOnce.Do(startAccessCacheInvalidationListener)
+}
+
+func startAccessCacheInvalidationListener() {
+	if db.Redis == nil {
+		return
+	}
+
+	go func() {
+		pubsub := db.Redis.Subscribe(
+			context.Background(),
+			storage.ConfigInvalidationChannel,
+			fileAccessInvalidationChannel,
+		)
+		defer func() {
+			_ = pubsub.Close()
+		}()
+
+		for range pubsub.Channel() {
+			ResetAccessCaches()
+		}
+	}()
+}
+
+// IsFilePublic reports whether uploadType is in the public access whitelist.
+func IsFilePublic(ctx context.Context, uploadType string) bool {
+	whitelist := loadFileAccessWhitelist(ctx)
+	_, ok := whitelist[strings.ToLower(uploadType)]
+	return ok
+}
+
+func loadFileAccessWhitelist(ctx context.Context) map[string]struct{} {
+	ensureAccessCacheListener()
+
+	fileAccessWhitelistMu.RLock()
+	if fileAccessWhitelistValid && time.Since(fileAccessWhitelistCheckedAt) < time.Duration(shared.AccessCacheTTL)*time.Second {
+		types := fileAccessWhitelistTypes
+		fileAccessWhitelistMu.RUnlock()
+		return types
+	}
+	fileAccessWhitelistMu.RUnlock()
+
+	fileAccessWhitelistMu.Lock()
+	defer fileAccessWhitelistMu.Unlock()
+
+	if fileAccessWhitelistValid && time.Since(fileAccessWhitelistCheckedAt) < time.Duration(shared.AccessCacheTTL)*time.Second {
+		return fileAccessWhitelistTypes
+	}
+
+	fileAccessWhitelistTypes = fetchFileAccessWhitelist(ctx)
+	fileAccessWhitelistValid = true
+	fileAccessWhitelistCheckedAt = time.Now()
+	return fileAccessWhitelistTypes
+}
+
+func fetchFileAccessWhitelist(ctx context.Context) map[string]struct{} {
+	whitelist := parseFileAccessWhitelist(ctx)
+	types := make(map[string]struct{}, len(whitelist))
+	for _, item := range whitelist {
+		types[strings.ToLower(item)] = struct{}{}
+	}
+	return types
+}
+
+func parseFileAccessWhitelist(ctx context.Context) []string {
+	var sc model.SystemConfig
+	if err := sc.GetByKey(ctx, model.ConfigKeyFileAccessWhitelist); err != nil || sc.Value == "" {
+		return []string{shared.DefaultPublicUploadType}
+	}
+
+	var whitelist []string
+	if err := json.Unmarshal([]byte(sc.Value), &whitelist); err == nil && len(whitelist) > 0 {
+		return whitelist
+	}
+
+	whitelist = parseCommaSeparatedWhitelist(sc.Value)
+	if len(whitelist) == 0 {
+		return []string{shared.DefaultPublicUploadType}
+	}
+	return whitelist
+}
+
+func parseCommaSeparatedWhitelist(value string) []string {
+	parts := strings.Split(value, ",")
+	whitelist := make([]string, 0, len(parts))
+	for _, part := range parts {
+		part = strings.TrimSpace(part)
+		if part != "" {
+			whitelist = append(whitelist, part)
+		}
+	}
+	return whitelist
+}