fix: implement constrained prompts matching tool-calling behavior

- Add exact format requirements to each question type
- Enforce word limits (15-25 words per response)
- Specify response patterns like 'This is a [noun/verb]' format
- Reduce max_tokens from 100 to 50 for concise responses
- Match the quality and constraint of original tool-calling approach

src/aiService.js

@@ -44,12 +44,12 @@ class OpenRouterService {
           model: this.model,
           messages: [{
             role: 'system',
-            content: 'You provide clues for word puzzles. Give useful information about grammar, meaning, or context. Keep responses short and focused. Never reveal the actual word.'
+            content: 'You provide clues for word puzzles. Follow the EXACT format requested. Be concise and direct. Never reveal the actual word. Stick to the word limits specified.'
           }, {
             role: 'user',
             content: prompt
           }],
-          max_tokens: 100,
+          max_tokens: 50,
           temperature: 0.6
         })
       });

src/conversationManager.js

@@ -104,10 +104,13 @@ class ChatService {
     const baseContext = `From "${bookTitle}" by ${author}: "${sentence}"`;
     
     const prompts = {
-      part_of_speech: `${baseContext}\n\nWhat part of speech is the missing word? Look at the sentence structure.`,
-      sentence_role: `${baseContext}\n\nWhat grammatical role does the missing word play? How does it function in the sentence?`,
-      word_category: `${baseContext}\n\nIs the missing word concrete or abstract? What type of concept does it represent?`,
-      synonym: `${baseContext}\n\nWhat's a related word or concept that would fit in this blank?`
+      part_of_speech: `${baseContext}\n\nRespond with exactly this format: "This is a [noun/verb/adjective/adverb]" then add one simple, concrete clue about what type (e.g., "a thing", "an action", "describes something"). Keep it under 20 words total.`,
+      
+      sentence_role: `${baseContext}\n\nPoint to specific words around the blank. Example format: "Look at 'the [words before] ____ [words after]' - what could [function]?" Focus only on the immediate context. Keep under 25 words.`,
+      
+      word_category: `${baseContext}\n\nStart with exactly: "This is abstract" or "This is concrete." Then give one relatable example or size clue: "Think about something very [big/small]" or "Like [feelings/objects]". Keep under 20 words total.`,
+      
+      synonym: `${baseContext}\n\nUse this format: "Try a word similar to [related word]" or "Think of another word for [meaning]". Give direct synonyms or word families only. Keep under 15 words.`
     };
     
     return prompts[questionType] || `${baseContext}\n\nProvide a helpful hint about the missing word without revealing it.`;