chore: remove iFlow-related modules and dependencies

- Deleted `iflow` provider implementation, including thinking configuration (`apply.go`) and authentication modules.
- Removed iFlow-specific tests, executors, and helpers across SDK and internal components.
- Updated all references to exclude iFlow functionality.

internal/registry/model_updater.go

@@ -213,7 +213,6 @@ func detectChangedProviders(oldData, newData *staticModelsJSON) []string {
 		{"codex", oldData.CodexTeam, newData.CodexTeam},
 		{"codex", oldData.CodexPlus, newData.CodexPlus},
 		{"codex", oldData.CodexPro, newData.CodexPro},
-		{"iflow", oldData.IFlow, newData.IFlow},
 		{"kimi", oldData.Kimi, newData.Kimi},
 		{"antigravity", oldData.Antigravity, newData.Antigravity},
 	}
@@ -334,7 +333,6 @@ func validateModelsCatalog(data *staticModelsJSON) error {
 		{name: "codex-team", models: data.CodexTeam},
 		{name: "codex-plus", models: data.CodexPlus},
 		{name: "codex-pro", models: data.CodexPro},
-		{name: "iflow", models: data.IFlow},
 		{name: "kimi", models: data.Kimi},
 		{name: "antigravity", models: data.Antigravity},
 	}