Make an unlocker's ID the name of its directory (closes #98)

Keychain and Secure Enclave unlocker IDs were the creation time to the
minute plus the host name, and passphrase unlocker IDs the time to the
minute, so two created within one minute shared an ID, and `unlocker
select`, `unlocker remove` and the selection after `unlocker add` acted on
the older one. Every unlocker's ID is now its directory name, unique in
its vault. PGP unlocker IDs were `pgp-<fingerprint>`; the check that
refuses a second PGP unlocker for one key now compares the fingerprint in
the other unlockers' metadata.

Model: opus-5-5

internal/cli/unlockers_corrupt_test.go

@@ -46,7 +46,7 @@ func TestUnlockerSelectSkipsCorruptUnlocker(t *testing.T) {
 	fs := newCorruptUnlockerVault(t)
 	instance, _ := newTestInstance(fs)
 
-	require.NoError(t, instance.UnlockerSelect("pgp-"+listTestGPGKeyID+"B"))
+	require.NoError(t, instance.UnlockerSelect(listTestUnlockerDirTwo))
 
 	current, err := afero.ReadFile(fs,
 		filepath.Join(testVaultDir(listTestVaultName), "current-unlocker"))
@@ -72,7 +72,7 @@ func TestUnlockerRemoveWithCorruptUnlocker(t *testing.T) {
 	}{
 		{
 			name:        "the other unlocker",
-			unlockerID:  "pgp-" + listTestGPGKeyID + "B",
+			unlockerID:  listTestUnlockerDirTwo,
 			wantLast:    true,
 			wantEntries: []string{listTestUnlockerDirOne},
 		},