feat: OpenRouter-ready AI service — all 11 methods implemented

IAIService:
+ generateMatchExplanation, summarizeTradeOffs, generateDataQualitySummary,
  classifyMarketSignal (4 new methods covering all documented AI output types)

OpenRouterAIService:
- All 11 methods now make real API calls via withFallback() pattern
- Every fallback is explicit (console.warn/error) — no silent mock bleed-through
- Proper JSON extraction with type-safe parsers, no any casts
- parseNeed: AI JSON → ParseNeedResult mapping (no TODO stubs)
- generateFollowUpQuestions, generateMatchExplanation, summarizeTradeOffs,
  generateDataQualitySummary, classifyMarketSignal, generateOfferEmail,
  extractCriteria, generateFollowUp: fully implemented

Prompts: +followUpQuestionsPrompt, +tradeOffPrompt, +dataQualityPrompt, +marketSignalPrompt

Factory (index.ts):
- VITE_AI_PROVIDER=mock|openrouter (new, takes priority)
- VITE_USE_REAL_AI=true still supported (legacy compat)
- Missing API key → explicit console.warn + MockAIService fallback

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/ai/index.ts

@@ -1,20 +1,44 @@
 /**
  * AI Service Factory
  *
- * Selects the active implementation based on the VITE_USE_REAL_AI feature flag.
+ * Provider selection (priority order):
+ *   1. VITE_AI_PROVIDER=openrouter  → OpenRouterAIService (requires VITE_OPENROUTER_API_KEY)
+ *   2. VITE_AI_PROVIDER=mock        → MockAIService (deterministic, no API key required)
+ *   3. VITE_USE_REAL_AI=true        → OpenRouterAIService (legacy flag, requires VITE_OPENROUTER_API_KEY)
+ *   4. (default)                    → MockAIService
  *
- * Mock mode (default):  no API key required, all responses are deterministic.
- * Real mode:            set VITE_USE_REAL_AI=true + VITE_OPENROUTER_API_KEY in .env
+ * If VITE_AI_PROVIDER=openrouter but VITE_OPENROUTER_API_KEY is missing, the factory
+ * logs a warning and falls back to MockAIService — never silently fails.
+ *
+ * Optional: VITE_OPENROUTER_MODEL controls which model OpenRouter uses.
+ * Default: anthropic/claude-3-5-haiku
  */
 import { MockAIService } from './mock/MockAIService'
 import { OpenRouterAIService } from './openrouter/OpenRouterAIService'
 import type { IAIService } from './IAIService'
 
-const useRealAI = import.meta.env.VITE_USE_REAL_AI === 'true'
-  && !!import.meta.env.VITE_OPENROUTER_API_KEY
+function resolveProvider(): IAIService {
+  const provider = import.meta.env.VITE_AI_PROVIDER as string | undefined
+  const legacyRealAI = import.meta.env.VITE_USE_REAL_AI === 'true'
+  const apiKey = import.meta.env.VITE_OPENROUTER_API_KEY as string | undefined
 
-export const aiService: IAIService = useRealAI ? OpenRouterAIService : MockAIService
+  const wantsOpenRouter = provider === 'openrouter' || (legacyRealAI && !provider)
+
+  if (wantsOpenRouter) {
+    if (!apiKey) {
+      console.warn(
+        '[aiService] OpenRouter selected but VITE_OPENROUTER_API_KEY is missing — falling back to MockAIService.',
+        'Set VITE_AI_PROVIDER=mock to suppress this warning.',
+      )
+      return MockAIService
+    }
+    return OpenRouterAIService
+  }
+
+  return MockAIService
+}
+
+export const aiService: IAIService = resolveProvider()
 
-// Named export so callers can reach the concrete impl when needed
 export { MockAIService, OpenRouterAIService }
 export type { IAIService }