Extract _ensure_conf_dir(); call it from both _save_credentials and _write_webdav_conf

Guarantees /etc/micronas is created with 750 root:www-data on any
code path that writes config — first-time setup OR first WebDAV share.
Fixes fresh-install permission issue without manual chmod.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -49,8 +49,7 @@ def _verify_password(password):
 
 def _save_credentials(user, password):
     h = _hash_password(password)
-    os.makedirs(_CONF_DIR, mode=0o750, exist_ok=True)
-    subprocess.run(['chown', 'root:www-data', _CONF_DIR], capture_output=True)
+    _ensure_conf_dir()
     Path(_ENV_FILE).write_text(f'MICRONAS_USER={user}\nMICRONAS_PASS_HASH={h}\n')
     os.chmod(_ENV_FILE, 0o600)
     _creds['user']  = user
@@ -321,7 +320,14 @@ def _parse_webdav_conf():
     return shares
 
 
+def _ensure_conf_dir():
+    """Create /etc/micronas with correct ownership so Apache can traverse it."""
+    os.makedirs(_CONF_DIR, mode=0o750, exist_ok=True)
+    subprocess.run(['chown', 'root:www-data', _CONF_DIR], capture_output=True)
+
+
 def _write_webdav_conf(shares):
+    _ensure_conf_dir()
     os.makedirs('/var/lib/apache2/webdav', exist_ok=True)
     lines = ['# Managed by MicroNAS — do not edit manually\n\n',
              'DavLockDB /var/lib/apache2/webdav/DavLock\n\n']