feat(repo): sync forks on the server, wire forks into clones, validate set-default

repo sync OWNER/REPO, run where no Git remote points to the repository,
now updates it on the server: a fork's branch fast-forwards to its
parent's through merge-upstream, and a pull mirror fetches its source.

repo fork reports an existing fork ("! bob/x already exists") instead of
a raw HTTP 409, refuses to fork a repository into its own owner, and
gains --fork-name, --clone (Git flags after --) and --remote, which adds
the fork as origin and renames the old origin to upstream.

repo clone passes Git flags after --, and takes --upstream-remote-name
and --no-upstream for forks. Clones report what they set up.

repo set-default checks that the repository exists before saving it,
prints the saved repository with --view, removes it with --unset, and
reports the change.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/repos_test.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"context"
 	"net/http"
+	"strings"
 	"testing"
 	"time"
 
@@ -104,6 +105,44 @@ View this repository on Gitea: https://gitea.test/bob/project
 		"clone:\thttps://gitea.test/bob/project.git\nssh:\t\nurl:\thttps://gitea.test/bob/project\n--\nHello **there**\n", out.String())
 }
 
+func TestRepoSetDefaultValidatesTheRepository(t *testing.T) {
+	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/repos/alice/project" {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		_, _ = w.Write([]byte(`{"full_name":"alice/project"}`))
+	}))
+	defer server.Close()
+	deps, _, diagnostics := repoTTYDeps(t, server.URL)
+	saved := "config --local tea.repository " + server.URL + "/alice/project"
+	runner := &fakeGit{results: map[string]string{"rev-parse --is-inside-work-tree": "true", saved: ""}}
+	deps.Git = runner
+	err := Execute(context.Background(), deps, []string{"repo", "set-default", "nobody/none"})
+	require.Error(t, err)
+	require.NotContains(t, strings.Join(runner.calls, "\n"), "config --local tea.repository")
+	require.NoError(t, Execute(context.Background(), deps, []string{"repo", "set-default", "alice/project"}))
+	require.Contains(t, runner.calls, saved)
+	require.Equal(t, "✓ Set alice/project as the default repository for this clone\n", diagnostics.String())
+}
+
+func TestRepoSetDefaultViewAndUnset(t *testing.T) {
+	deps, out, diagnostics := repoTTYDeps(t, "http://gitea.test")
+	runner := &fakeGit{results: map[string]string{
+		"rev-parse --is-inside-work-tree":       "true",
+		"config --local --get tea.repository":   "http://gitea.test/alice/project",
+		"config --local --unset tea.repository": "",
+	}}
+	deps.Git = runner
+	require.NoError(t, Execute(context.Background(), deps, []string{"repo", "set-default", "--view"}))
+	require.Equal(t, "http://gitea.test/alice/project\n", out.String())
+	require.NoError(t, Execute(context.Background(), deps, []string{"repo", "set-default", "-u"}))
+	require.Equal(t, "✓ Removed the default repository http://gitea.test/alice/project from this clone\n", diagnostics.String())
+	deps.Git = &fakeGit{}
+	err := Execute(context.Background(), deps, []string{"repo", "set-default", "-v"})
+	require.ErrorContains(t, err, "set-default must run inside a Git clone")
+}
+
 func TestRepoViewOfAnEmptyRepositorySkipsTheReadme(t *testing.T) {
 	server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		require.Equal(t, "/api/v1/repos/alice/empty", r.URL.Path)