Raise Go to the latest release, update dependencies, use the standard library uuid, add a vulnerability check (closes #102)

Go 1.27.1 in go.mod and in the Dockerfile's test and build images.
Every module go.mod requires is at its current release; protoc-gen-go
follows protobuf to v1.36.12 and mf.pb.go is regenerated. The standard
library uuid package replaces github.com/google/uuid; FromBytes could
only fail on a length validateUUID already checks, so that call and its
unreachable error are gone. make vulncheck runs govulncheck v1.8.0,
installed with go install at its release commit, in a vulncheck stage
of the Dockerfile; script/check does not run it. The newer go directive
switches on lint checks for strings.SplitSeq and t.Chdir, now used. A
new test pins the bytes of a seeded manifest written by an mfer built
before this change.

Model: opus-5-5

internal/cli/entry_test.go

@@ -354,6 +354,39 @@ func TestGenerateCommand(t *testing.T) {
 	assert.True(t, exists)
 }
 
+// TestGenerateSeededManifestBytes pins the exact bytes `gen --seed` writes
+// for a fixed tree, so that a Go or dependency update that changes what
+// mfer writes fails here. testdata/seeded.mf was written by an mfer built
+// before such an update. The tree has enough files that zstd compresses
+// the manifest instead of storing it as it is.
+func TestGenerateSeededManifestBytes(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	start := time.Date(2025, 6, 1, 0, 0, 0, 0, time.UTC)
+
+	for i := range 200 {
+		path := fmt.Sprintf("/testdir/d%d/f%03d.txt", i%10, i)
+		mtime := start.Add(time.Duration(i) * time.Second)
+
+		require.NoError(t, fs.MkdirAll(filepath.Dir(path), 0o755))
+		writeTestFile(t, fs, path, fmt.Sprintf("file %d\n", i))
+		require.NoError(t, fs.Chtimes(path, mtime, mtime))
+	}
+
+	opts := testOpts([]string{
+		testApp, cmdGenerate, "-q", "--seed", "mfer", "-o", testOutput, testDir,
+	}, fs)
+	require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+	got, err := afero.ReadFile(fs, testOutput)
+	require.NoError(t, err)
+
+	want, err := os.ReadFile("testdata/seeded.mf")
+	require.NoError(t, err)
+	assert.Equal(t, want, got)
+}
+
 func TestGenerateAndCheckCommand(t *testing.T) {
 	t.Parallel()
 
@@ -410,7 +443,7 @@ func TestGenerateRecordsModeOnlyWhenAsked(t *testing.T) {
 		listed := map[string]string{}
 		out := strings.TrimSuffix(testStdout(t, opts), "\n")
 
-		for _, line := range strings.Split(out, "\n") {
+		for line := range strings.SplitSeq(out, "\n") {
 			fields := strings.Split(line, "\t") // mode, size, mtime, path
 			require.Len(t, fields, 4, line)
 			listed[fields[3]] = fields[0]