feat: add GitHub Copilot provider

Copilot device login + onboarding option; model list auth detection.

src/providers/github-copilot-token.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, it, vi } from "vitest";
+
+const loadJsonFile = vi.fn();
+const saveJsonFile = vi.fn();
+const resolveStateDir = vi.fn().mockReturnValue("/tmp/clawdbot-state");
+
+vi.mock("../infra/json-file.js", () => ({
+  loadJsonFile,
+  saveJsonFile,
+}));
+
+vi.mock("../config/paths.js", () => ({
+  resolveStateDir,
+}));
+
+describe("github-copilot token", () => {
+  it("derives baseUrl from token", async () => {
+    const { deriveCopilotApiBaseUrlFromToken } = await import(
+      "./github-copilot-token.js"
+    );
+
+    expect(
+      deriveCopilotApiBaseUrlFromToken("token;proxy-ep=proxy.example.com;"),
+    ).toBe("https://api.example.com");
+    expect(
+      deriveCopilotApiBaseUrlFromToken("token;proxy-ep=https://proxy.foo.bar;"),
+    ).toBe("https://api.foo.bar");
+  });
+
+  it("uses cache when token is still valid", async () => {
+    const now = Date.now();
+    loadJsonFile.mockReturnValue({
+      token: "cached;proxy-ep=proxy.example.com;",
+      expiresAt: now + 60 * 60 * 1000,
+      updatedAt: now,
+    });
+
+    const { resolveCopilotApiToken } = await import(
+      "./github-copilot-token.js"
+    );
+
+    const fetchImpl = vi.fn();
+    const res = await resolveCopilotApiToken({
+      githubToken: "gh",
+      fetchImpl: fetchImpl as unknown as typeof fetch,
+    });
+
+    expect(res.token).toBe("cached;proxy-ep=proxy.example.com;");
+    expect(res.baseUrl).toBe("https://api.example.com");
+    expect(String(res.source)).toContain("cache:");
+    expect(fetchImpl).not.toHaveBeenCalled();
+  });
+
+  it("fetches and stores token when cache is missing", async () => {
+    loadJsonFile.mockReturnValue(undefined);
+
+    const fetchImpl = vi.fn().mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: async () => ({
+        token: "fresh;proxy-ep=https://proxy.contoso.test;",
+        expires_at: Math.floor(Date.now() / 1000) + 3600,
+      }),
+    });
+
+    const { resolveCopilotApiToken } = await import(
+      "./github-copilot-token.js"
+    );
+
+    const res = await resolveCopilotApiToken({
+      githubToken: "gh",
+      fetchImpl: fetchImpl as unknown as typeof fetch,
+    });
+
+    expect(res.token).toBe("fresh;proxy-ep=https://proxy.contoso.test;");
+    expect(res.baseUrl).toBe("https://api.contoso.test");
+    expect(saveJsonFile).toHaveBeenCalledTimes(1);
+  });
+});