fix: use deep merge for config updates and save inputs on blur

- Backend: replace shallow merge with recursive deepMerge in PUT /api/hermes/config
  to prevent nested config fields from being lost when updating partial values
- Frontend: switch all NInput fields to default-value + @change (save on blur)
  instead of :value + @update:value (save on every keystroke) in both
  PlatformSettings.vue and SettingsView.vue api_server tab
- Remove unused debounce logic and dead changeKey function

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

packages/server/src/routes/hermes/config.ts

@@ -79,6 +79,20 @@ function getNested(obj: Record<string, any>, path: string): any {
   return cur
 }
 
+function deepMerge(target: Record<string, any>, source: Record<string, any>): Record<string, any> {
+  for (const key of Object.keys(source)) {
+    if (
+      source[key] && typeof source[key] === 'object' && !Array.isArray(source[key]) &&
+      target[key] && typeof target[key] === 'object' && !Array.isArray(target[key])
+    ) {
+      target[key] = deepMerge(target[key], source[key])
+    } else {
+      target[key] = source[key]
+    }
+  }
+  return target
+}
+
 async function readEnvPlatforms(): Promise<Record<string, any>> {
   try {
     const raw = await readFile(envPath(), 'utf-8')
@@ -217,7 +231,7 @@ configRoutes.put('/api/hermes/config', async (ctx) => {
 
   try {
     const config = await readConfig()
-    config[section] = { ...(config[section] || {}), ...values }
+    config[section] = deepMerge(config[section] || {}, values)
     await writeConfig(config)
     // Restart gateway for platform/channel config changes
     if (PLATFORM_SECTIONS.has(section)) {