feat: add clean aiService.js without hardcoded keys

- Clean implementation using only environment variables
- OPENROUTER_API_KEY and HF_API_KEY from HuggingFace secrets
- No hardcoded API keys in source code

src/aiService.js

@@ -0,0 +1,104 @@
+class OpenRouterService {
+  constructor() {
+    this.apiUrl = 'https://openrouter.ai/api/v1/chat/completions';
+    this.apiKey = this.getApiKey();
+    this.model = 'google/gemma-3-27b-it:free';
+  }
+
+  getApiKey() {
+    if (typeof process !== 'undefined' && process.env && process.env.OPENROUTER_API_KEY) {
+      return process.env.OPENROUTER_API_KEY;
+    }
+    if (typeof window !== 'undefined' && window.OPENROUTER_API_KEY) {
+      return window.OPENROUTER_API_KEY;
+    }
+    return '';
+  }
+
+  setApiKey(key) {
+    this.apiKey = key;
+  }
+
+  async getContextualHint(passage, wordToReplace, context) {
+    if (!this.apiKey) {
+      return 'API key required for contextual hints';
+    }
+
+    try {
+      const response = await fetch(this.apiUrl, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': `Bearer ${this.apiKey}`,
+          'HTTP-Referer': window.location.origin,
+          'X-Title': 'Cloze Reader'
+        },
+        body: JSON.stringify({
+          model: this.model,
+          messages: [{
+            role: 'user',
+            content: `In this passage: "${passage}"
+            
+The word "${wordToReplace}" has been replaced with a blank. Give me a helpful hint about what word fits here, considering the context: "${context}".
+
+Provide a brief, educational hint that helps understand the word without giving it away directly.`
+          }],
+          max_tokens: 150,
+          temperature: 0.7
+        })
+      });
+
+      if (!response.ok) {
+        throw new Error(`API request failed: ${response.status}`);
+      }
+
+      const data = await response.json();
+      return data.choices[0].message.content.trim();
+    } catch (error) {
+      console.error('Error getting contextual hint:', error);
+      return 'Unable to generate hint at this time';
+    }
+  }
+
+  async getContextualization(title, author, passage) {
+    if (!this.apiKey) {
+      return `📚 Practice with classic literature from ${author}'s "${title}"`;
+    }
+
+    try {
+      const response = await fetch(this.apiUrl, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': `Bearer ${this.apiKey}`,
+          'HTTP-Referer': window.location.origin,
+          'X-Title': 'Cloze Reader'
+        },
+        body: JSON.stringify({
+          model: this.model,
+          messages: [{
+            role: 'system',
+            content: 'You are a literary expert providing brief educational context about classic literature. Always respond with exactly 2 sentences, no more. Avoid exaggerative adverbs. Be factual and restrained.'
+          }, {
+            role: 'user',
+            content: `Provide educational context for this passage from "${title}" by ${author}: "${passage}"`
+          }],
+          max_tokens: 100,
+          temperature: 0.3
+        })
+      });
+
+      if (!response.ok) {
+        throw new Error(`API request failed: ${response.status}`);
+      }
+
+      const data = await response.json();
+      return data.choices[0].message.content.trim();
+    } catch (error) {
+      console.error('Error getting contextualization:', error);
+      return `📚 Practice with classic literature from ${author}'s "${title}"`;
+    }
+  }
+}
+
+export { OpenRouterService as AIService };