fix: resolve React Error #310 and refactor admin section

- Fix React bug #33580: remove Suspense boundaries co-located with Link components
- Delete settings/loading.tsx and admin/loading.tsx (root cause of race condition)
- Convert all admin navigation from Next.js Link to anchor tags
- Move admin pages to dedicated (admin) route group
- Add AdminHeader matching main header visual design
- Add AdminSidebar with anchor-based navigation
- Add /api/admin/models route handler (replaces server actions for GET)
- Add /api/debug/client-error for server-side browser error reporting
- Add useNoteRefreshOptional() to fix crash in AdminHeader
- Hide Admin Dashboard menu for non-admin users
- Change app icons from yellow to blue (#3A7CA5) matching brand primary
- Fix admin search bar width to match main header

Made-with: Cursor

memento-note/lib/config.ts

@@ -1,16 +1,36 @@
 import prisma from './prisma'
 
+// Environment variable fallbacks for system config keys
+const ENV_FALLBACKS: Record<string, string> = {
+  AI_PROVIDER_TAGS: process.env.AI_PROVIDER_TAGS || '',
+  AI_MODEL_TAGS: process.env.AI_MODEL_TAGS || '',
+  AI_PROVIDER_EMBEDDING: process.env.AI_PROVIDER_EMBEDDING || '',
+  AI_MODEL_EMBEDDING: process.env.AI_MODEL_EMBEDDING || '',
+  AI_PROVIDER_CHAT: process.env.AI_PROVIDER_CHAT || '',
+  AI_MODEL_CHAT: process.env.AI_MODEL_CHAT || '',
+  OLLAMA_BASE_URL: process.env.OLLAMA_BASE_URL || '',
+  OPENAI_API_KEY: process.env.OPENAI_API_KEY || '',
+  CUSTOM_OPENAI_API_KEY: process.env.CUSTOM_OPENAI_API_KEY || '',
+  CUSTOM_OPENAI_BASE_URL: process.env.CUSTOM_OPENAI_BASE_URL || '',
+  ALLOW_REGISTRATION: process.env.ALLOW_REGISTRATION || '',
+  NEXTAUTH_URL: process.env.NEXTAUTH_URL || '',
+}
+
 export async function getSystemConfig() {
+  let dbConfig: Record<string, string> = {}
   try {
     const configs = await prisma.systemConfig.findMany()
-    return configs.reduce((acc, conf) => {
+    dbConfig = configs.reduce((acc, conf) => {
       acc[conf.key] = conf.value
       return acc
     }, {} as Record<string, string>)
   } catch (e) {
     console.error('Failed to load system config from DB:', e)
-    return {}
   }
+
+  // Merge: DB values take precedence, env vars as fallback
+  const merged = { ...ENV_FALLBACKS, ...dbConfig }
+  return merged
 }
 
 /**