feat(ai): implement intelligent auto-tagging system

- Added multi-provider AI infrastructure (OpenAI/Ollama)
- Implemented real-time tag suggestions with debounced analysis
- Created AI diagnostics and database maintenance tools in Settings
- Added automated garbage collection for orphan labels
- Refined UX with deterministic color hashing and interactive ghost tags

keep-notes/lib/ai/providers/openai.ts

@@ -0,0 +1,46 @@
+import { openai } from '@ai-sdk/openai';
+import { generateObject, embed } from 'ai';
+import { z } from 'zod';
+import { AIProvider, TagSuggestion } from '../types';
+
+export class OpenAIProvider implements AIProvider {
+  private model: any;
+
+  constructor(apiKey: string, modelName: string = 'gpt-4o-mini') {
+    this.model = openai(modelName);
+  }
+
+  async generateTags(content: string): Promise<TagSuggestion[]> {
+    try {
+      const { object } = await generateObject({
+        model: this.model,
+        schema: z.object({
+          tags: z.array(z.object({
+            tag: z.string().describe('Le nom du tag, court et en minuscules'),
+            confidence: z.number().min(0).max(1).describe('Le niveau de confiance entre 0 et 1')
+          }))
+        }),
+        prompt: `Analyse la note suivante et suggère entre 1 et 5 tags pertinents. 
+        Contenu de la note: "${content}"`,
+      });
+
+      return object.tags;
+    } catch (e) {
+      console.error('Erreur génération tags OpenAI:', e);
+      return [];
+    }
+  }
+
+  async getEmbeddings(text: string): Promise<number[]> {
+    try {
+      const { embedding } = await embed({
+        model: openai.embedding('text-embedding-3-small'),
+        value: text,
+      });
+      return embedding;
+    } catch (e) {
+      console.error('Erreur embeddings OpenAI:', e);
+      return [];
+    }
+  }
+}