feat: 新增 git retime，把指定日期范围的提交时间改到 21:00-23:00 并强推

- 保留每个提交的原日期，只重排时分秒到 21:00-23:00；同日严格递增，
  间隔 5-40 分钟且秒位随机；窗口不足时自动压紧并在预览中标注
- 支持 --window/--since/--until、--interval（含 match-remote）、--seed、
  --remote、--branch、--no-push
- 安全措施：默认只预览（退出码 2）、脏工作区拒绝、改写前创建
  refs/kopsc-backup/<分支>-<时间戳> 备份、推送前比对 tree 哈希、
  只用 --force-with-lease
- BuiltinRequest 增加 Confirmed，使内置命令能获知 CLI 已确认 --yes
- 文档：新增 README.git.md，主 README 补充导航与示例

internal/executor/gitlog_test.go

@@ -0,0 +1,134 @@
+package executor
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+	"time"
+)
+
+// gitResponse is one canned git result.
+type gitResponse struct {
+	out, errOut string
+	err         error
+}
+
+// fakeGitRunner answers git invocations from a table keyed by the joined args.
+type fakeGitRunner struct {
+	responses map[string]gitResponse
+	calls     []string
+	envs      []([]string)
+}
+
+func (f *fakeGitRunner) Run(ctx context.Context, args ...string) (string, string, error) {
+	return f.RunEnv(ctx, nil, args...)
+}
+
+// RunEnv records the environment it was given so tests can assert on the
+// author/committer dates passed to git commit-tree.
+func (f *fakeGitRunner) RunEnv(ctx context.Context, env []string, args ...string) (string, string, error) {
+	key := strings.Join(args, " ")
+	f.calls = append(f.calls, key)
+	if len(env) > 0 {
+		f.envs = append(f.envs, env)
+	}
+	if r, ok := f.responses[key]; ok {
+		return r.out, r.errOut, r.err
+	}
+	return "", "unexpected git call: " + key, errors.New("exit status 1")
+}
+
+func TestParseGitLog(t *testing.T) {
+	out := "aaaa1111\t4f2a1b0\t2026-10-01T21:07:43+08:00\t2026-10-01T21:07:43+08:00\tfeat: 初始提交\n" +
+		"bbbb2222\t9c6f072\t2026-10-02T22:32:11+08:00\t2026-10-02T22:33:00+08:00\tdocs: 补充说明\n"
+
+	commits, err := parseGitLog(out)
+	if err != nil {
+		t.Fatalf("parseGitLog: %v", err)
+	}
+	if len(commits) != 2 {
+		t.Fatalf("parsed %d commits, want 2", len(commits))
+	}
+
+	first := commits[0]
+	if first.Hash != "aaaa1111" || first.Short != "4f2a1b0" || first.Subject != "feat: 初始提交" {
+		t.Errorf("first = %+v", first)
+	}
+	// Times keep their seconds, which the retiming relies on.
+	if first.AuthorTime.Second() != 43 || first.AuthorTime.Hour() != 21 || first.AuthorTime.Minute() != 7 {
+		t.Errorf("author time lost precision: %v", first.AuthorTime)
+	}
+	if commits[1].CommitTime.After(commits[1].AuthorTime) != true {
+		t.Errorf("committer time not parsed: %v", commits[1].CommitTime)
+	}
+}
+
+func TestParseGitLogSkipsTrailingBlankLine(t *testing.T) {
+	out := "aaaa\t4f2\t2026-10-01T21:07:43+08:00\t2026-10-01T21:07:43+08:00\tsubject\n\n"
+	commits, err := parseGitLog(out)
+	if err != nil || len(commits) != 1 {
+		t.Fatalf("commits = %v, err = %v", commits, err)
+	}
+}
+
+func TestParseGitLogKeepsTabsInSubject(t *testing.T) {
+	// SplitN with limit 5 keeps anything the subject contains, tabs included.
+	out := "aaaa\t4f2\t2026-10-01T21:00:00+08:00\t2026-10-01T21:00:00+08:00\tsub\twith\ttabs\n"
+	commits, err := parseGitLog(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if commits[0].Subject != "sub\twith\ttabs" {
+		t.Errorf("subject = %q", commits[0].Subject)
+	}
+}
+
+func TestParseGitLogRejectsBrokenInput(t *testing.T) {
+	if _, err := parseGitLog("not-enough-fields\n"); err == nil {
+		t.Error("expected an error for a short record")
+	}
+	bad := "a\tb\tnot-a-time\t2026-10-01T21:00:00+08:00\ts\n"
+	if _, err := parseGitLog(bad); err == nil || !strings.Contains(err.Error(), "作者时间") {
+		t.Errorf("err = %v, want an author-time error", err)
+	}
+}
+
+func TestGitCommitDate(t *testing.T) {
+	loc := time.FixedZone("CST", 8*3600)
+	c := gitCommit{AuthorTime: time.Date(2026, 10, 5, 21, 7, 43, 0, loc)}
+	d := c.Date()
+	if d.Hour() != 0 || d.Minute() != 0 || d.Day() != 5 || d.Month() != time.October || d.Year() != 2026 {
+		t.Fatalf("Date() = %v", d)
+	}
+	if d.Location() != loc {
+		t.Errorf("Date() lost the original time zone: %v", d.Location())
+	}
+}
+
+func TestListCommitsRunsGitLog(t *testing.T) {
+	runner := &fakeGitRunner{responses: map[string]gitResponse{
+		"log --format=" + gitLogFormat + " main": {
+			out: "aaaa\t4f2\t2026-10-01T21:00:00+08:00\t2026-10-01T21:00:00+08:00\tsubject\n",
+		},
+	}}
+	commits, err := listCommits(context.Background(), runner, "main")
+	if err != nil {
+		t.Fatalf("listCommits: %v", err)
+	}
+	if len(commits) != 1 || commits[0].Short != "4f2" {
+		t.Fatalf("commits = %+v", commits)
+	}
+}
+
+func TestListCommitsReportsGitFailure(t *testing.T) {
+	runner := &fakeGitRunner{responses: map[string]gitResponse{
+		"log --format=" + gitLogFormat + " main": {
+			errOut: "fatal: not a git repository", err: errors.New("exit status 128"),
+		},
+	}}
+	_, err := listCommits(context.Background(), runner, "main")
+	if err == nil || !strings.Contains(err.Error(), "not a git repository") {
+		t.Fatalf("err = %v, want git's stderr", err)
+	}
+}