fix: merge 30 general improvements from release branch

Bug fixes:
- Detached context for GetAccountConcurrencyBatch (prevent all-zero on request cancel)
- Filter soft-deleted users in GetByGroupID
- Stripe CSP policy (allow Stripe.js in script-src and frame-src)
- WebSearch API key validation on save
- RECHARGING status in payment result success check
- Windows test fixes (logger Sync deadlock, config path escaping)

Feature enhancements:
- Webhook multi-instance dispatch (extractOutTradeNo + GetWebhookProvider)
- EasyPay mobile H5 payment (device param + PayURL2)
- SSE error propagation in WebSearch emulation
- AccountStatsCost DTO field for admin usage logs
- Plans sort by sort_order instead of created_at
- UsageMapHook for streaming response usage data
- apicompat Instructions field passthrough
- EffectiveLoadFactor for ops concurrency/metrics
- Usage billing RETURNING balance for notify system
- BulkUpdate mixed channel warning with details
- println to slog migration in auth cache
- Wire ProviderSet cleanup
- CI cache-dependency-path optimization

Frontend:
- Refund eligibility check per provider (canRequestRefund)
- Plan sort_order editing
- Dead code cleanup (simulate_claude_max, client_affinity)
- GroupsView platform switch guard
- channels features_config API type
- UsageView account_stats_cost export

backend/internal/repository/user_group_rate_repo.go

@@ -100,7 +100,7 @@ func (r *userGroupRateRepository) GetByGroupID(ctx context.Context, groupID int6
 	query := `
 		SELECT ugr.user_id, u.username, u.email, COALESCE(u.notes, ''), u.status, ugr.rate_multiplier
 		FROM user_group_rate_multipliers ugr
-		JOIN users u ON u.id = ugr.user_id
+		JOIN users u ON u.id = ugr.user_id AND u.deleted_at IS NULL
 		WHERE ugr.group_id = $1
 		ORDER BY ugr.user_id
 	`