Move the command line from cmd/bsdaily into internal/cli (closes #8)

cmd/bsdaily/main.go now only passes Version to cli.Main and exits with
the status it returns, as REPO_POLICIES.md requires of cmd/. The cobra
command, the flag rules and the date parsing moved unchanged into
internal/cli, so flags, help text, error messages, exit status and the
first log line stay as they were. The fallback to dev for an empty
version moved with them into cli.Main.

parseTargetDates is exported as ParseTargetDates so that a table test
outside the package can reach it; the test never touches the filesystem
or runs the extraction. README describes the new layout and TODO.md
records the step.

Model: opus-5-5

internal/cli/dates_test.go

@@ -0,0 +1,109 @@
+package cli_test
+
+import (
+	"slices"
+	"strings"
+	"testing"
+
+	"git.eeqj.de/sneak/bsdaily/internal/cli"
+)
+
+func TestParseTargetDates(t *testing.T) {
+	t.Parallel()
+
+	const oneDay = "2026-05-14"
+
+	// want lists the expected days as YYYY-MM-DD.
+	tests := []struct {
+		name string
+		date string
+		from string
+		to   string
+		want []string
+	}{
+		{name: "no flags"},
+		{name: "single date", date: "2026-06-27", want: []string{"2026-06-27"}},
+		{
+			name: "range across a month end", from: "2026-06-29", to: "2026-07-02",
+			want: []string{"2026-06-29", "2026-06-30", "2026-07-01", "2026-07-02"},
+		},
+		{name: "range of one day", from: oneDay, to: oneDay, want: []string{oneDay}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := cli.ParseTargetDates(tt.date, tt.from, tt.to)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			days := make([]string, 0, len(got))
+			for _, day := range got {
+				days = append(days, day.Format("2006-01-02"))
+			}
+
+			if !slices.Equal(days, tt.want) {
+				t.Errorf("days = %v, want %v", days, tt.want)
+			}
+		})
+	}
+}
+
+func TestParseTargetDatesErrors(t *testing.T) {
+	t.Parallel()
+
+	// wantErr is how the error message starts: for a malformed date, the
+	// date parser's own explanation follows it.
+	tests := []struct {
+		name    string
+		date    string
+		from    string
+		to      string
+		wantErr string
+	}{
+		{
+			name: "from after to", from: "2026-03-02", to: "2026-03-01",
+			wantErr: "--from 2026-03-02 is after --to 2026-03-01",
+		},
+		{name: "from without to", from: "2026-04-01", wantErr: "--from requires --to"},
+		{name: "to without from", to: "2026-04-02", wantErr: "--to requires --from"},
+		{
+			name: "date with from", date: "2026-01-05", from: "2026-01-06",
+			wantErr: "--date and --from/--to are mutually exclusive",
+		},
+		{
+			name: "date with from and to", date: "2026-01-07",
+			from: "2026-01-08", to: "2026-01-09",
+			wantErr: "--date and --from/--to are mutually exclusive",
+		},
+		{
+			name: "malformed date", date: "27.06.2026",
+			wantErr: `invalid --date "27.06.2026" (expected YYYY-MM-DD): `,
+		},
+		{
+			name: "date that does not exist", date: "2026-02-30",
+			wantErr: `invalid --date "2026-02-30" (expected YYYY-MM-DD): `,
+		},
+		{
+			name: "malformed from", from: "2026-1-10", to: "2026-01-11",
+			wantErr: `invalid --from "2026-1-10" (expected YYYY-MM-DD): `,
+		},
+		{
+			name: "malformed to", from: "2026-01-12", to: "tomorrow",
+			wantErr: `invalid --to "tomorrow" (expected YYYY-MM-DD): `,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := cli.ParseTargetDates(tt.date, tt.from, tt.to)
+			if err == nil || !strings.HasPrefix(err.Error(), tt.wantErr) {
+				t.Errorf("error = %v, want one starting %q", err, tt.wantErr)
+			}
+		})
+	}
+}