Give -v to verbose, move --version to -V (closes #64)

urfave/cli's built-in version flag claimed -v, so "mfer -v --version"
failed to parse, and -v meant version at the root but verbose on
generate, check, freshen and fetch. Verbose is the more common meaning,
so the root now takes -v and -q too, the version flag takes -V, and a
-v or -q before the subcommand name applies to that subcommand.

User-visible changes: -v alone prints help with verbose logging, not
the version; use -V or --version. "mfer version" prints "mfer version
0.1.0 (...)", the same line as --version, instead of the bare
"0.1.0 (...)".

The error-message tests now send their log lines to io.Discard; they
were landing in other tests' output buffers.

Model: opus-4-8 (implementation); opus-5-5 (rework)

internal/cli/errmsg_test.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"context"
 	"flag"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -16,6 +17,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	urfcli "github.com/urfave/cli/v2"
+	"sneak.berlin/go/mfer/internal/log"
 	"sneak.berlin/go/mfer/mfer"
 )
 
@@ -36,12 +38,16 @@ const (
 	msgFpB = "BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB"
 )
 
-// runLocked runs fn while holding runMu, so operations that write to the
-// process-global logger do not race the other CLI runs.
+// runLocked runs fn while holding runMu and with the process-global logger
+// pointed at io.Discard, so fn's log lines neither race the other CLI runs
+// nor land in the last run's buffers, which its test may still be reading.
 func runLocked(fn func() error) error {
 	runMu.Lock()
 	defer runMu.Unlock()
 
+	log.SetOutput(io.Discard, io.Discard)
+	log.Init()
+
 	return fn()
 }