[keyman] thread the configured keys and tmp directories through encrypt/decrypt

encryptKeys and decryptKeys each took `vaultDir` and rebuilt `<vault>/keys`
and `<vault>/tmp` from it, so `keysDir` and `tmpDir` in .keymanrc.json were
honoured by main and list and silently ignored by the two operations that
write. main was also passing vaultRoot where encrypt expected the keys
directory, which put encrypted keys one level above where list looks for
them: with any config at all, a key encrypted a second ago was invisible.

Both now take keysDir and tmpDir explicitly. The decrypt location prompt
names the real directories instead of the hardcoded `vault/tmp` and
`~/.ssh`, which meant its labels were also its values — hence LOCAL_MODE.

tests/vault-layout.test.ts is the regression: encrypt then list, driven
through keyman() with only age and the prompts mocked, against a config
using keysDir `encrypted` and tmpDir `plain`. Every unit suite passed
through this bug because each was told which directory to use; the seam
between them was untested. Verified it fails when main is reverted to pass
vaultRoot.

packages/keyman/src/keyman.main.ts

@@ -95,12 +95,12 @@ export async function keyman() {
       case 'encrypt': {
         const pubkey = await ageRecipient();
         if (pubkey) {
-          await encryptKeys(sshDir, paths.vaultRoot, paths.tmpDir, pubkey);
+          await encryptKeys(sshDir, paths.keysDir, paths.tmpDir, pubkey);
         }
         break;
       }
       case 'decrypt':
-        await decryptKeys(sshDir, paths.vaultRoot, paths.keyPath);
+        await decryptKeys(sshDir, paths.keysDir, paths.tmpDir, paths.keyPath);
         break;
       case 'quit':
         console.log('\n👋 Goodbye!\n');