Move the command tree into internal/cli (closes #8)

cmd/simplexcalc/ now holds only main.go: it passes the version the
linker sets to cli.Main and exits with the status that returns. root.go
and run.go move to internal/cli with their comments, changed only to
take the version as a parameter. Main reads the process's arguments and
output; execute takes them as parameters so the new tests can check the
version line and the non-zero status of an unknown command. Commands,
flags, output, log lines and exit status are unchanged, and the
-X main.version flag in the Dockerfile still applies.

Model: opus-5-5

internal/cli/run.go

@@ -0,0 +1,58 @@
+package cli
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/signal"
+	"runtime"
+	"syscall"
+
+	"github.com/spf13/cobra"
+	"sneak.berlin/go/simplexcalc/internal/bot"
+	"sneak.berlin/go/simplexcalc/internal/config"
+	"sneak.berlin/go/simplexcalc/internal/logger"
+)
+
+func runCmd(version string) *cobra.Command {
+	return &cobra.Command{
+		Use:   "run",
+		Short: "run the bot",
+		Args:  cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			return run(cmd.Context(), version)
+		},
+	}
+}
+
+// run reads the configuration and runs the bot until SIGINT or SIGTERM,
+// or until it fails. A failure is the process's exit status, so a
+// supervisor restarts it.
+func run(ctx context.Context, version string) error {
+	cfg, err := config.New()
+	if err != nil {
+		return fmt.Errorf("reading configuration: %w", err)
+	}
+
+	log := logger.New(os.Stdout, cfg.Debug)
+	log.Info("starting",
+		"appname", appname,
+		"version", version,
+		"arch", runtime.GOARCH,
+		"data_dir", cfg.DataDir,
+	)
+
+	ctx, stop := signal.NotifyContext(ctx, syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	err = bot.Run(ctx, log, cfg.DataDir)
+	if err != nil {
+		log.Error("stopped", "error", err)
+
+		return err
+	}
+
+	log.Info("stopped")
+
+	return nil
+}