feat: AI Writer inline — génère du contenu au curseur

- Mode 'write' ajouté à paragraph-refactor.service.ts
- Endpoint /api/ai/reformulate étendu (option 'write' + writePrompt)
- UI : champ de prompt inline apparaît au curseur après slash menu
  - Tape / → 'Écrire avec l'IA' → décrit ce que tu veux → Entrée
  - L'IA génère et insère le contenu à la position du curseur
- Pas de migration DB, réutilise l'infra existante
- i18n FR/EN

memento-note/lib/ai/services/paragraph-refactor.service.ts

@@ -10,7 +10,7 @@ import { LanguageDetectionService } from './language-detection.service'
 import { getTagsProvider } from '../factory'
 import { getSystemConfig } from '@/lib/config'
 
-export type RefactorMode = 'clarify' | 'shorten' | 'improveStyle' | 'fix_grammar' | 'translate' | 'explain'
+export type RefactorMode = 'clarify' | 'shorten' | 'improveStyle' | 'fix_grammar' | 'translate' | 'explain' | 'write'
 
 export interface RefactorOption {
   mode: RefactorMode
@@ -69,24 +69,29 @@ export class ParagraphRefactorService {
     content: string,
     mode: RefactorMode,
     format: 'html' | 'markdown' = 'markdown',
-    targetLanguage?: string
+    targetLanguage?: string,
+    writePrompt?: string
   ): Promise<RefactorResult> {
-    // Validate word count
-    const wordCount = content.split(/\s+/).length
-    if (wordCount < this.MIN_WORDS || wordCount > this.MAX_WORDS) {
-      throw new Error(
-        `Please select ${this.MIN_WORDS}-${this.MAX_WORDS} words to reformulate`
-      )
+    // 'write' mode skips word count validation (generates from prompt, no selection needed)
+    if (mode !== 'write') {
+      const wordCount = content.split(/\s+/).length
+      if (wordCount < this.MIN_WORDS || wordCount > this.MAX_WORDS) {
+        throw new Error(
+          `Please select ${this.MIN_WORDS}-${this.MAX_WORDS} words to reformulate`
+        )
+      }
     }
 
     // Detect language or use provided target language
-    const { language: detectedLanguage } = await this.languageDetection.detectLanguage(content)
+    const { language: detectedLanguage } = mode === 'write'
+      ? { language: targetLanguage || 'fr' }
+      : await this.languageDetection.detectLanguage(content)
     const language = targetLanguage || detectedLanguage
 
     try {
       // Build prompts
       const systemPrompt = this.getSystemPrompt(mode, format)
-      const userPrompt = this.getUserPrompt(mode, content, language, format)
+      const userPrompt = this.getUserPrompt(mode, content, language, format, writePrompt)
 
       // Get AI provider from factory
       const config = await getSystemConfig()
@@ -99,10 +104,10 @@ export class ParagraphRefactorService {
       // Calculate word count change
       const refactoredWordCount = refactored.split(/\s+/).length
       const wordCountChange = {
-        original: wordCount,
+        original: mode === 'write' ? 0 : content.split(/\s+/).length,
         refactored: refactoredWordCount,
-        difference: refactoredWordCount - wordCount,
-        percentage: ((refactoredWordCount - wordCount) / wordCount) * 100
+        difference: refactoredWordCount - (mode === 'write' ? 0 : content.split(/\s+/).length),
+        percentage: 0
       }
 
       return {
@@ -252,7 +257,13 @@ Your goal: Explain the selected text, concept, or word clearly and concisely.
 Provide context, definitions, or relevant information to help the user understand it.
 
 CRITICAL LANGUAGE RULE: You MUST explain it in the requested language (which is the user's interface language).
-Keep it concise but informative.${formatInstruction}`
+Keep it concise but informative.${formatInstruction}`,
+
+      write: `You are an expert writer and content creator.
+Your goal: Write new content based on the user's instruction. Be clear, well-structured, and informative.
+Write naturally in the requested language.
+
+If context is provided (note title or surrounding text), use it to make the content relevant.${formatInstruction}`
     }
 
     return prompts[mode]
@@ -261,7 +272,7 @@ Keep it concise but informative.${formatInstruction}`
   /**
    * Get mode-specific user prompt
    */
-  private getUserPrompt(mode: RefactorMode, content: string, language: string, format: 'html' | 'markdown' = 'markdown'): string {
+  private getUserPrompt(mode: RefactorMode, content: string, language: string, format: 'html' | 'markdown' = 'markdown', writePrompt?: string): string {
     const instructions = {
       clarify: `IMPORTANT: The text below is in ${language}. Your response MUST be in ${language}. Do NOT translate to English.
 
@@ -283,7 +294,20 @@ Please fix any spelling, grammar, or punctuation errors in this ${language} text
 Only return the translated text, nothing else.`,
 
       explain: `Please explain the following text/concept in ${language}.
-Keep the explanation clear, educational, and concise.`
+Keep the explanation clear, educational, and concise.`,
+
+      write: `Write the following in ${language}. Only return the content, no meta-commentary.`
+    }
+
+    if (mode === 'write') {
+      const suffix = `CRITICAL: Respond ONLY with the generated content in ${language}. No explanations, no meta-commentary. Format strictly as ${format === 'html' ? 'HTML tags' : 'Markdown'}.`
+      const contextPart = content.trim() ? `\n\nContext (note: "${content.trim().slice(0, 100)}"):\n` : ''
+      return `${instructions.write}
+
+${writePrompt || 'Write a paragraph about the current topic.'}
+
+${contextPart}
+${suffix}`
     }
 
     const systemSuffix = mode === 'explain'