chore: remove Qwen support from SDK and internal components

- Deleted `QwenAuthenticator`, internal `qwen_auth`, and `qwen_executor` implementations.
- Removed all Qwen-related OAuth flows, token handling, and execution logic.
- Cleaned up dependencies and references to Qwen across the codebase.

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},
-		{"qwen", oldData.Qwen, newData.Qwen},
 		{"iflow", oldData.IFlow, newData.IFlow},
 		{"kimi", oldData.Kimi, newData.Kimi},
 		{"antigravity", oldData.Antigravity, newData.Antigravity},
@@ -335,7 +334,6 @@ func validateModelsCatalog(data *staticModelsJSON) error {
 		{name: "codex-team", models: data.CodexTeam},
 		{name: "codex-plus", models: data.CodexPlus},
 		{name: "codex-pro", models: data.CodexPro},
-		{name: "qwen", models: data.Qwen},
 		{name: "iflow", models: data.IFlow},
 		{name: "kimi", models: data.Kimi},
 		{name: "antigravity", models: data.Antigravity},