fix: remove Ollama default fallbacks in factory and Docker

ROOT CAUSE: The factory was defaulting to 'ollama' when no provider
was configured, and docker-compose.yml was always setting OLLAMA_BASE_URL
even when using OpenAI. This caused the app to try connecting to Ollama
even when OpenAI was configured in the admin.

CRITICAL CHANGES:
1. lib/ai/factory.ts - Removed 'ollama' default fallback
   - getTagsProvider() now throws error if AI_PROVIDER_TAGS not set
   - getEmbeddingsProvider() now throws error if AI_PROVIDER_EMBEDDING not set
   - Forces explicit configuration instead of silent fallback to Ollama

2. docker-compose.yml - Removed default OLLAMA_BASE_URL
   - Changed: OLLAMA_BASE_URL=${OLLAMA_BASE_URL:-http://ollama:11434}
   - To: OLLAMA_BASE_URL=${OLLAMA_BASE_URL}
   - Only set if explicitly defined in .env.docker

3. Application name: Mento → Memento (correct spelling)
   - Updated in: sidebar, README, deploy.sh, DOCKER_DEPLOYMENT.md

4. app/api/ai/config/route.ts - Return 'not set' instead of 'ollama'
   - Makes it clear when provider is not configured

IMPACT: The app will now properly use OpenAI when configured in the
admin interface, instead of silently falling back to Ollama.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

keep-notes/components/sidebar.tsx

@@ -79,7 +79,7 @@ export function Sidebar({ className, user }: { className?: string, user?: any })
             <StickyNote className="h-5 w-5" />
           </div>
           <div className="flex flex-col">
-            <span className="text-lg font-bold tracking-tight text-slate-900 dark:text-white leading-none">Mento</span>
+            <span className="text-lg font-bold tracking-tight text-slate-900 dark:text-white leading-none">Memento</span>
             <span className="text-[10px] font-medium text-slate-400 dark:text-slate-500 uppercase tracking-widest mt-1">{t('nav.workspace')}</span>
           </div>
         </div>