feat: Add default and advanced install method selection

- Add ConfigurationModal component for selecting default or advanced installation mode
- Default mode: Uses predefined defaults with minimal user input (hostname from slug, vmbr0, dhcp, etc.)
- Advanced mode: Full configuration modal with all environment variables customizable
- Add support for IPv4 CIDR input when network mode is 'static'
- Add support for IPv6 static address input when IPv6 method is 'static'
- Implement password formatting as '-password <password>' for build.func compatibility
- Auto-enable SSH when password or SSH keys are provided
- Add storage selection dropdowns filtered by server node assignment
- Pass environment variables through entire execution stack (frontend -> WebSocket -> SSH/local execution)
- Add mode environment variable (always set to 'default' for script execution)
- Update ExecutionModeModal to show 'Advanced (Beta)' option

server.js

@@ -82,6 +82,7 @@ const handle = app.getRequestHandler();
  * @property {number} [cloneCount]
  * @property {string[]} [hostnames]
  * @property {'lxc'|'vm'} [containerType]
+ * @property {Record<string, string|number|boolean>} [envVars]
  */
 
 class ScriptExecutionHandler {
@@ -421,7 +422,9 @@ class ScriptExecutionHandler {
       // Add envVars to environment
       if (envVars && typeof envVars === 'object') {
         for (const [key, value] of Object.entries(envVars)) {
-          envWithVars[key] = String(value);
+          /** @type {Record<string, string>} */
+          const envRecord = envWithVars;
+          envRecord[key] = String(value);
         }
       }