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/openai_model_mapping_test.go

@@ -91,6 +91,7 @@ func TestNormalizeCodexModel(t *testing.T) {
 		"gpt-5.3-codex-spark-high":  "gpt-5.3-codex-spark",
 		"gpt-5.3-codex-spark-xhigh": "gpt-5.3-codex-spark",
 		"gpt-5.3":                   "gpt-5.3-codex",
+		"gpt-image-2":               "gpt-image-2",
 	}
 
 	for input, expected := range cases {