feat(ConfigurationModal): add Container ID (CTID) and DNS Search Domain to advanced install

- Add optional Container ID (CTID) field at top of advanced form (var_ctid)
- Add DNS Search Domain field in Network section (var_searchdomain)
- Validate CTID when set: integer >= 100; empty = use next available ID
- Both fields optional; empty values omitted from env so script uses defaults

src/app/_components/ConfigurationModal.tsx

@@ -88,6 +88,7 @@ export function ConfigurationModal({
         var_mtu: 1500,
         var_mac: '',
         var_ns: '',
+        var_searchdomain: '',
 
         // Identity
         var_hostname: slug,
@@ -214,7 +215,7 @@ export function ConfigurationModal({
       }
       // Container ID (CTID): if set, must be integer >= 100
       const ctidVal = advancedVars.var_ctid;
-      if (ctidVal !== '' && ctidVal !== undefined) {
+      if (ctidVal !== '' && ctidVal !== undefined && typeof ctidVal !== 'boolean') {
         const ctidNum = typeof ctidVal === 'string' ? parseInt(ctidVal, 10) : ctidVal;
         if (isNaN(ctidNum) || ctidNum < 100) {
           newErrors.var_ctid = 'Must be 100 or greater';
@@ -656,6 +657,17 @@ export function ConfigurationModal({
                       <p className="mt-1 text-xs text-destructive">{errors.var_ns}</p>
                     )}
                   </div>
+                  <div>
+                    <label className="block text-sm font-medium text-foreground mb-2">
+                      DNS Search Domain
+                    </label>
+                    <Input
+                      type="text"
+                      value={typeof advancedVars.var_searchdomain === 'boolean' ? '' : String(advancedVars.var_searchdomain ?? '')}
+                      onChange={(e) => updateAdvancedVar('var_searchdomain', e.target.value)}
+                      placeholder="e.g. local, home.lan"
+                    />
+                  </div>
                 </div>
               </div>