revert: remove fork-only changes from release sync

Revert payment/wechat, sora/claude-max cleanup, fork-only migrations,
and cosmetic changes that were brought in by the release sync commit.
Keep only channel-monitor related improvements:
- PublicSettingsInjectionPayload named struct with drift test
- ChannelMonitorRunner graceful shutdown in wire
- image_output_price in SupportedModelChip
- Simplified buildSelfNavItems in AppSidebar
- Gateway WARN logs for 503 branches

backend/internal/service/error_policy_test.go

@@ -110,12 +110,13 @@ func TestCheckErrorPolicy(t *testing.T) {
 			expected:   ErrorPolicyTempUnscheduled,
 		},
 		{
-			// Gemini OAuth 401 second hit 会升级为 error（返回 None，交由默认错误逻辑处理）。
-			name: "temp_unschedulable_401_second_hit_gemini_escalates",
+			// Antigravity 401 不走升级逻辑（由 applyErrorPolicy 的 temp_unschedulable_rules 自行控制），
+			// second hit 仍然返回 TempUnscheduled。
+			name: "temp_unschedulable_401_second_hit_antigravity_stays_temp",
 			account: &Account{
 				ID:                      15,
 				Type:                    AccountTypeOAuth,
-				Platform:                PlatformGemini, // 非 Antigravity 平台 401 second hit 升级
+				Platform:                PlatformAntigravity,
 				TempUnschedulableReason: `{"status_code":401,"until_unix":1735689600}`,
 				Credentials: map[string]any{
 					"temp_unschedulable_enabled": true,
@@ -130,29 +131,7 @@ func TestCheckErrorPolicy(t *testing.T) {
 			},
 			statusCode: 401,
 			body:       []byte(`unauthorized`),
-			expected:   ErrorPolicyNone, // Gemini 401 second hit 升级为 error
-		},
-		{
-			name: "temp_unschedulable_401_antigravity_no_escalation",
-			account: &Account{
-				ID:                      16,
-				Type:                    AccountTypeOAuth,
-				Platform:                PlatformAntigravity, // Antigravity 跳过 401 升级，由 rules 正常处理
-				TempUnschedulableReason: `{"status_code":401,"until_unix":1735689600}`,
-				Credentials: map[string]any{
-					"temp_unschedulable_enabled": true,
-					"temp_unschedulable_rules": []any{
-						map[string]any{
-							"error_code":       float64(401),
-							"keywords":         []any{"unauthorized"},
-							"duration_minutes": float64(10),
-						},
-					},
-				},
-			},
-			statusCode: 401,
-			body:       []byte(`unauthorized`),
-			expected:   ErrorPolicyTempUnscheduled, // Antigravity 不升级，继续走规则匹配
+			expected:   ErrorPolicyTempUnscheduled,
 		},
 		{
 			name: "temp_unschedulable_body_miss_returns_none",