sync: bring over remaining release/custom-0.1.115 changes

- Extract PublicSettingsInjectionPayload named struct with drift test
- Add channel_monitor_default_interval_seconds to SSR injection
- Add image_output_price to SupportedModelChip
- Simplify AppSidebar buildSelfNavItems (admins see available channels)
- Add gateway WARN logs for 503 no-available-accounts branches
- Wire ChannelMonitorRunner into provideCleanup for graceful shutdown
- Add migrations 130/131 (CC template userid fix + mimicry field cleanup)
- Clean up fork-only features (sora, claude max simulation, client affinity)
- Remove ~320 obsolete i18n keys
- Add codexUsage utility, WechatServiceButton, BulkEditAccountModal
- Tidy go.sum

backend/internal/service/openai_model_mapping_test.go

@@ -91,7 +91,6 @@ 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 {