feat: Add OpenRouter as AI provider with easy switch

- Added openrouter.ts with provider configuration
- Default provider: OpenRouter with google/gemma-3-27b-it
- Switch to Gemini via AI_PROVIDER=gemini in .env.local
- Both providers use same credit system
- OpenRouter uses OpenAI-compatible API

To switch providers, set in .env.local:
AI_PROVIDER=openrouter  # default
AI_PROVIDER=gemini      # Google Gemini

src/lib/openrouter.ts

@@ -0,0 +1,40 @@
+import OpenAI from 'openai';
+
+/**
+ * AI Provider configuration
+ * 
+ * Set AI_PROVIDER in .env.local to switch:
+ * - "openrouter" (default) - Uses OpenRouter with Gemma 3 27B
+ * - "gemini" - Uses Google Gemini 2.5 Flash
+ */
+export type AIProvider = 'openrouter' | 'gemini';
+
+export function getAIProvider(): AIProvider {
+    const provider = process.env.AI_PROVIDER?.toLowerCase();
+    if (provider === 'gemini') return 'gemini';
+    return 'openrouter'; // Default
+}
+
+/**
+ * OpenRouter client for vision tasks
+ * Uses OpenAI-compatible API
+ */
+export function getOpenRouterClient(): OpenAI {
+    const apiKey = process.env.OPENROUTER_API_KEY;
+
+    if (!apiKey) {
+        throw new Error('OPENROUTER_API_KEY is not configured.');
+    }
+
+    return new OpenAI({
+        baseURL: 'https://openrouter.ai/api/v1',
+        apiKey: apiKey,
+        defaultHeaders: {
+            'HTTP-Referer': 'https://whiskyvault.app',
+            'X-Title': 'WhiskyVault',
+        },
+    });
+}
+
+// Default OpenRouter model for vision tasks
+export const OPENROUTER_VISION_MODEL = 'google/gemma-3-27b-it';