feat: 實作 bear CLI PAT 模式 MVP（login/whoami/token/logout/status）

- 新增 Elixir + Mix escript 專案（Req 0.5+、Jason）
- login --token <PAT>：以 PAT 驗證 /userinfo 後寫入憑證檔（0600）
- whoami：GET /userinfo 顯示身分 claims（支援 --json）
- token：印出 access token 供 pipe（--refresh 在 PAT 模式忽略）
- logout：清除本機憑證；status：純本機判定
- 憑證檔採原子寫入（rename）、0600、O_CREAT|O_EXCL 防 symlink
- 全域選項：--issuer/--config/--json/-v/-h/--version
- 29 個單元測試；mix precommit（compile --warnings-as-errors + format + test）
- 更新 README.md 與 docs/commands.md 反映 PAT 模式 MVP

Device Flow 登入待伺服器端 P1（bear 倉庫）完成後再接。issue #2

test/bear_cli/cli_test.exs

@@ -0,0 +1,200 @@
+defmodule BearCli.CLITest do
+  use ExUnit.Case, async: false
+
+  alias BearCli.CLI
+
+  setup do
+    old_creds = System.get_env("BEAR_CREDENTIALS")
+
+    on_exit(fn ->
+      restore_env("BEAR_CREDENTIALS", old_creds)
+    end)
+
+    :ok
+  end
+
+  describe "parse/1" do
+    test "no args -> help" do
+      assert {:help, %{}} = CLI.parse([])
+    end
+
+    test "--version" do
+      assert {:version, %{}} = CLI.parse(["--version"])
+    end
+
+    test "-h alias -> help" do
+      assert {:help, %{}} = CLI.parse(["-h"])
+    end
+
+    test "login --token X" do
+      assert {:ok, :login, %{token: "X"}} = CLI.parse(["login", "--token", "X"])
+    end
+
+    test "global option before command" do
+      assert {:ok, :whoami, %{json: true}} = CLI.parse(["--json", "whoami"])
+    end
+
+    test "global option after command" do
+      assert {:ok, :status, %{json: true}} = CLI.parse(["status", "--json"])
+    end
+
+    test "token --refresh" do
+      assert {:ok, :token, %{refresh: true}} = CLI.parse(["token", "--refresh"])
+    end
+
+    test "issuer flag is captured" do
+      assert {:ok, :whoami, %{issuer: "https://x"}} =
+               CLI.parse(["whoami", "--issuer", "https://x"])
+    end
+
+    test "unknown command -> usage error" do
+      assert {:error, _, 2} = CLI.parse(["frobnicate"])
+    end
+
+    test "unknown option -> usage error" do
+      assert {:error, _, 2} = CLI.parse(["--bogus"])
+    end
+  end
+
+  describe "dispatch/2 (injected api)" do
+    test "login --token writes credentials and prints email" do
+      path = tmp_path()
+      on_exit(fn -> File.rm(path) end)
+      System.put_env("BEAR_CREDENTIALS", path)
+
+      {code, out} =
+        ExUnit.CaptureIO.with_io(fn ->
+          CLI.dispatch(CLI.parse(["login", "--token", "good"]), api: fake_api())
+        end)
+
+      assert code == 0
+      assert out =~ "已登入：alice@example.com"
+      assert {:ok, %{"access_token" => "good"}} = BearCli.Credentials.load(path)
+    end
+
+    test "login with invalid token exits 1" do
+      System.put_env("BEAR_CREDENTIALS", tmp_path())
+
+      {code, err} =
+        ExUnit.CaptureIO.with_io(
+          :stderr,
+          "",
+          fn -> CLI.dispatch(CLI.parse(["login", "--token", "bad"]), api: fake_api()) end
+        )
+
+      assert code == 1
+      assert err =~ "token 無效"
+    end
+
+    test "login without --token points to Device Flow being unavailable" do
+      System.put_env("BEAR_CREDENTIALS", tmp_path())
+
+      {code, err} =
+        ExUnit.CaptureIO.with_io(
+          :stderr,
+          "",
+          fn -> CLI.dispatch(CLI.parse(["login"]), api: fake_api()) end
+        )
+
+      assert code == 2
+      assert err =~ "Device Flow"
+    end
+
+    test "whoami when not logged in exits 3" do
+      System.put_env("BEAR_CREDENTIALS", "/nonexistent/credentials.json")
+
+      {code, err} =
+        ExUnit.CaptureIO.with_io(
+          :stderr,
+          "",
+          fn -> CLI.dispatch(CLI.parse(["whoami"]), api: fake_api()) end
+        )
+
+      assert code == 3
+      assert err =~ "未登入"
+    end
+
+    test "whoami prints claims" do
+      path = tmp_path()
+      on_exit(fn -> File.rm(path) end)
+      System.put_env("BEAR_CREDENTIALS", path)
+      BearCli.Credentials.save(%{"issuer" => "https://x", "access_token" => "good"}, path)
+
+      {code, out} =
+        ExUnit.CaptureIO.with_io(fn ->
+          CLI.dispatch(CLI.parse(["whoami"]), api: fake_api())
+        end)
+
+      assert code == 0
+      assert out =~ "email"
+      assert out =~ "alice@example.com"
+    end
+
+    test "token prints only the token" do
+      path = tmp_path()
+      on_exit(fn -> File.rm(path) end)
+      System.put_env("BEAR_CREDENTIALS", path)
+      BearCli.Credentials.save(%{"issuer" => "https://x", "access_token" => "good-token"}, path)
+
+      {code, out} =
+        ExUnit.CaptureIO.with_io(fn ->
+          CLI.dispatch(CLI.parse(["token"]), api: fake_api())
+        end)
+
+      assert code == 0
+      assert String.trim(out) == "good-token"
+    end
+
+    test "status when logged in exits 0 and reports PAT mode" do
+      path = tmp_path()
+      on_exit(fn -> File.rm(path) end)
+      System.put_env("BEAR_CREDENTIALS", path)
+
+      BearCli.Credentials.save(
+        %{"issuer" => "https://x", "email" => "a@b.c", "access_token" => "t"},
+        path
+      )
+
+      {code, out} =
+        ExUnit.CaptureIO.with_io(fn ->
+          CLI.dispatch(CLI.parse(["status"]), api: fake_api())
+        end)
+
+      assert code == 0
+      assert out =~ "已登入：a@b.c"
+      assert out =~ "PAT"
+    end
+
+    test "logout clears credentials" do
+      path = tmp_path()
+      on_exit(fn -> File.rm(path) end)
+      System.put_env("BEAR_CREDENTIALS", path)
+      BearCli.Credentials.save(%{"issuer" => "https://x", "access_token" => "t"}, path)
+
+      {code, _out} =
+        ExUnit.CaptureIO.with_io(fn ->
+          CLI.dispatch(CLI.parse(["logout"]), api: fake_api())
+        end)
+
+      assert code == 0
+      assert :error == BearCli.Credentials.load(path)
+    end
+  end
+
+  defp fake_api do
+    fn _issuer, token ->
+      case token do
+        "good" -> {:ok, %{"sub" => "u1", "email" => "alice@example.com", "name" => "Alice"}}
+        "bad" -> {:error, :unauthorized, "invalid_token"}
+        _ -> {:error, :server_error, 500}
+      end
+    end
+  end
+
+  defp tmp_path do
+    Path.join(System.tmp_dir!(), "bear_cli_cli_#{System.unique_integer([:positive])}.json")
+  end
+
+  defp restore_env(key, nil), do: System.delete_env(key)
+  defp restore_env(key, value), do: System.put_env(key, value)
+end