feat(providers): add APIFree support

Add APIFree as a built-in OpenAI-compatible provider. APIFree offers
agent-optimised models such as skywork-ai/skyclaw-v1 through an
OpenAI-compatible API at https://api.apifree.ai/agent/v1.

Changes:
- Register apifree provider in the provider registry
- Add config schema field
- Add documentation with configuration example
- Add provider tests, websocket channel tests, and webui tests
- Add provider icon in settings UI

webui/src/components/settings/SettingsView.tsx

@@ -2150,6 +2150,7 @@ const PROVIDER_ICONS: Record<string, LucideIcon> = {
   byteplus_coding_plan: Cloud,
   qianfan: Database,
   ant_ling: Sparkles,
+  apifree: Sparkles,
   azure_openai: Cloud,
   bedrock: Database,
   vllm: Cpu,

webui/src/tests/app-layout.test.tsx

@@ -580,6 +580,13 @@ describe("App layout", () => {
                   api_key_required: true,
                   default_api_base: "https://api.ant-ling.com/v1",
                 },
+                {
+                  name: "apifree",
+                  label: "APIFree",
+                  configured: false,
+                  api_key_required: true,
+                  default_api_base: "https://api.apifree.ai/agent/v1",
+                },
                 {
                   name: "azure_openai",
                   label: "Azure OpenAI",
@@ -739,6 +746,7 @@ describe("App layout", () => {
     fireEvent.click(within(settingsNav).getByRole("button", { name: "Providers" }));
     expect(screen.getByText("OpenRouter")).toBeInTheDocument();
     expect(screen.getByText("Ant Ling")).toBeInTheDocument();
+    expect(screen.getByText("APIFree")).toBeInTheDocument();
     expect(screen.getAllByText("Not configured").length).toBeGreaterThan(0);
     fireEvent.click(screen.getByText("OpenAI"));
     fireEvent.click(screen.getByRole("button", { name: "Edit" }));
@@ -751,6 +759,8 @@ describe("App layout", () => {
     expect(screen.queryByDisplayValue("unsaved-openai-key")).not.toBeInTheDocument();
     fireEvent.click(screen.getByText("Ant Ling"));
     expect(screen.getByDisplayValue("https://api.ant-ling.com/v1")).toBeInTheDocument();
+    fireEvent.click(screen.getByText("APIFree"));
+    expect(screen.getByDisplayValue("https://api.apifree.ai/agent/v1")).toBeInTheDocument();
     fireEvent.click(screen.getByText("Atomic Chat"));
     expect(screen.getByDisplayValue("http://localhost:1337/v1")).toBeInTheDocument();
     expect(screen.getByRole("button", { name: "Save" })).toBeEnabled();