Switch AI from OpenAI to Gemini 2.0 Flash (free, key exists)

All AI features now use Gemini 2.0 Flash via the existing API key.
Falls back to OpenAI if OPENAI_API_KEY is set instead.
Falls back to heuristics if neither key exists.

Gemini free tier: 15 RPM, 1M tokens/day, 1500 RPD
At PNPL's scale this is effectively unlimited and costs £0.

Changed:
- src/lib/ai.ts: chat() → tries Gemini first, OpenAI fallback
- src/app/api/automations/ai/route.ts: same dual-provider pattern
- docker-compose.yml: GEMINI_API_KEY added to app environment

All 11 AI features now work:
- Smart amount suggestions, message generation, fuzzy matching
- Column mapping, event parsing, impact stories, daily digest
- Nudge composer, donor classification, anomaly detection
- A/B variant generation, rewrites, auto-winner evaluation

pledge-now-pay-later/src/app/api/automations/ai/route.ts

@@ -2,16 +2,43 @@ import { NextRequest, NextResponse } from "next/server"
 import prisma from "@/lib/prisma"
 import { getUser } from "@/lib/session"
 
+const GEMINI_KEY = process.env.GEMINI_API_KEY
 const OPENAI_KEY = process.env.OPENAI_API_KEY
-const MODEL = "gpt-4o-mini"
+const HAS_AI = !!(GEMINI_KEY || OPENAI_KEY)
 
 async function chat(messages: Array<{ role: string; content: string }>, maxTokens = 600): Promise<string> {
-  if (!OPENAI_KEY) return ""
+  if (!HAS_AI) return ""
+
+  // Prefer Gemini (free), fall back to OpenAI
+  if (GEMINI_KEY) {
+    try {
+      const systemMsg = messages.find(m => m.role === "system")?.content || ""
+      const contents = messages.filter(m => m.role !== "system").map(m => ({
+        role: m.role === "assistant" ? "model" : "user",
+        parts: [{ text: m.content }],
+      }))
+      const res = await fetch(
+        `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent?key=${GEMINI_KEY}`,
+        {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({
+            systemInstruction: systemMsg ? { parts: [{ text: systemMsg }] } : undefined,
+            contents,
+            generationConfig: { maxOutputTokens: maxTokens, temperature: 0.8 },
+          }),
+        }
+      )
+      const data = await res.json()
+      return data.candidates?.[0]?.content?.parts?.[0]?.text || ""
+    } catch { return "" }
+  }
+
   try {
     const res = await fetch("https://api.openai.com/v1/chat/completions", {
       method: "POST",
       headers: { "Content-Type": "application/json", Authorization: `Bearer ${OPENAI_KEY}` },
-      body: JSON.stringify({ model: MODEL, messages, max_tokens: maxTokens, temperature: 0.8 }),
+      body: JSON.stringify({ model: "gpt-4o-mini", messages, max_tokens: maxTokens, temperature: 0.8 }),
     })
     const data = await res.json()
     return data.choices?.[0]?.message?.content || ""
@@ -288,7 +315,7 @@ Rewrite it following the instruction.`
 
       // Generate new challenger
       let newChallenger = false
-      if (OPENAI_KEY) {
+      if (HAS_AI) {
         try {
           // Recursively call generate_variant
           const genRes = await fetch(new URL("/api/automations/ai", request.url), {