feat: Pro limit 2,500/mo, website templating, cleanup

- Set Pro tier limit to 2,500 PDFs/month (was unlimited/5000)
- Added Pro limit enforcement in usage middleware
- Updated landing page, JSON-LD, and Stripe product description
- Created build-time HTML templating (partials for nav/footer/styles)
- Source files in public/src/, partials in public/partials/
- Build script: node scripts/build-html.cjs
- Deleted stale backup file
- Fixed index.html nav logo to use <a> tag for consistency

dist/middleware/usage.js

@@ -2,6 +2,7 @@ import { isProKey } from "../services/keys.js";
 import logger from "../services/logger.js";
 import pool from "../services/db.js";
 const FREE_TIER_LIMIT = 100;
+const PRO_TIER_LIMIT = 5000;
 // In-memory cache, periodically synced to PostgreSQL
 let usage = new Map();
 function getMonthKey() {
@@ -36,6 +37,15 @@ export function usageMiddleware(req, res, next) {
     const key = keyInfo?.key || "unknown";
     const monthKey = getMonthKey();
     if (isProKey(key)) {
+        const record = usage.get(key);
+        if (record && record.monthKey === monthKey && record.count >= PRO_TIER_LIMIT) {
+            res.status(429).json({
+                error: "Pro tier limit reached (5,000/month). Contact support for higher limits.",
+                limit: PRO_TIER_LIMIT,
+                used: record.count,
+            });
+            return;
+        }
         trackUsage(key, monthKey);
         next();
         return;
@@ -46,7 +56,7 @@ export function usageMiddleware(req, res, next) {
             error: "Free tier limit reached",
             limit: FREE_TIER_LIMIT,
             used: record.count,
-            upgrade: "Upgrade to Pro for unlimited conversions: https://docfast.dev/pricing",
+            upgrade: "Upgrade to Pro for 5,000 PDFs/month: https://docfast.dev/pricing",
         });
         return;
     }