Add OpenAI-compatible AI investment advisor to benefit calculator

- server.js: add /api/calculate endpoint using openai SDK with configurable
  AI_API_URL, AI_API_KEY, AI_MODEL, AI_DEBUG env vars (works with any
  OpenAI-compatible provider: NVIDIA NIM, Together AI, Groq, Ollama, etc.)
- app.js: make calculator submit handler async; call /api/calculate with
  graceful fallback to client-side generated text if AI is unavailable
- package.json: add openai and dotenv dependencies
- AI_SETUP.md: rewrite to document new unified env var config with provider examples

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

server.js

@@ -14,9 +14,20 @@ const path    = require('path');
 const fs      = require('fs');
 const express = require('express');
 const Database = require('better-sqlite3');
+const OpenAI   = require('openai');
 
 // ── Config ──────────────────────────────────────────────
 const PORT    = process.env.PORT || 3000;
+
+// ── AI client (OpenAI-compatible) ────────────────────────
+const AI_API_URL = process.env.AI_API_URL || 'https://api.openai.com/v1';
+const AI_API_KEY = process.env.AI_API_KEY || '';
+const AI_MODEL   = process.env.AI_MODEL   || 'gpt-4o-mini';
+const AI_DEBUG   = process.env.AI_DEBUG   === 'true';
+
+const aiClient = AI_API_KEY
+  ? new OpenAI({ apiKey: AI_API_KEY, baseURL: AI_API_URL })
+  : null;
 const DB_DIR  = path.join(__dirname, 'data');
 const DB_PATH = path.join(DB_DIR, 'leads.db');
 
@@ -127,6 +138,60 @@ app.get('/api/leads', (req, res) => {
   res.json({ count: leads.length, leads });
 });
 
+// POST /api/calculate  — AI-powered investment recommendation
+app.post('/api/calculate', async (req, res) => {
+  if (!aiClient) {
+    return res.status(503).json({ error: 'AI service not configured.' });
+  }
+
+  const { homesites, propertyType, annualIncome, paymentFreq, reserveFunds, interest2025 } = req.body ?? {};
+
+  if (!homesites || !annualIncome) {
+    return res.status(400).json({ error: 'homesites and annualIncome are required.' });
+  }
+
+  const fmt       = n => '$' + Math.round(n).toLocaleString();
+  const freqLabel = { monthly: 'monthly', quarterly: 'quarterly', annually: 'annual' }[paymentFreq] || 'monthly';
+  const typeLabel = { sfh: 'single-family home', townhomes: 'townhome', condos: 'condo', mixed: 'mixed-use' }[propertyType] || '';
+
+  const prompt = `You are a conservative HOA financial advisor. Given the following community data, provide a brief (3-4 sentence) plain-English investment income recommendation. Use only conservative, realistic estimates. Do not speculate beyond what the data supports.
+
+Community: ${homesites}-unit ${typeLabel} association
+Annual dues income: ${fmt(annualIncome)} (collected ${freqLabel})
+Reserve fund balance: ${fmt(reserveFunds || 0)}
+Interest income earned in 2025: ${fmt(interest2025 || 0)}
+
+Provide a recommendation focused on:
+1. How much of the reserve funds could conservatively be invested and in what vehicle (e.g. CD ladder, money market, T-bills)
+2. How much operating cash could earn interest between collection and expense periods
+3. A realistic estimated annual interest income potential
+4. A single sentence comparing that to their 2025 actual if provided
+
+Keep the tone professional and factual. No bullet points — flowing paragraph only.`;
+
+  if (AI_DEBUG) {
+    console.log('[AI_DEBUG] model:', AI_MODEL);
+    console.log('[AI_DEBUG] prompt:', prompt);
+  }
+
+  try {
+    const completion = await aiClient.chat.completions.create({
+      model:      AI_MODEL,
+      max_tokens: 300,
+      messages:   [{ role: 'user', content: prompt }],
+    });
+
+    const text = completion.choices[0]?.message?.content ?? '';
+
+    if (AI_DEBUG) console.log('[AI_DEBUG] response:', text);
+
+    res.json({ recommendation: text });
+  } catch (err) {
+    console.error('AI API error:', err.message);
+    res.status(502).json({ error: 'AI service unavailable. Showing estimated result.' });
+  }
+});
+
 // Health check
 app.get('/api/health', (_req, res) => res.json({ status: 'ok', ts: new Date().toISOString() }));