fix: BUG-046 usage endpoint data leak, BUG-047 copy button, BUG-048 email change links

BUG-046 (CRITICAL): getUsageStats() now accepts apiKey param and returns
only that key usage instead of all users. Route passes req.apiKeyInfo.key.

BUG-047: Added visible Copy button to Pro key success page in billing.ts.

BUG-048: Added class="open-email-change" to Change Email links in all
HTML pages so the JS modal opener can find them.

src/index.ts

@@ -104,8 +104,8 @@ app.use("/v1/convert", authMiddleware, usageMiddleware, pdfRateLimitMiddleware,
 app.use("/v1/templates", authMiddleware, usageMiddleware, templatesRouter);
 
 // Admin: usage stats
-app.get("/v1/usage", authMiddleware, (_req, res) => {
-  res.json(getUsageStats());
+app.get("/v1/usage", authMiddleware, (req: any, res) => {
+  res.json(getUsageStats(req.apiKeyInfo?.key));
 });
 
 // Admin: concurrency stats

src/middleware/usage.ts

@@ -76,11 +76,14 @@ function trackUsage(key: string, monthKey: string): void {
   }
 }
 
-export function getUsageStats(): Record<string, { count: number; month: string }> {
+export function getUsageStats(apiKey?: string): Record<string, { count: number; month: string }> {
   const stats: Record<string, { count: number; month: string }> = {};
-  for (const [key, record] of usage) {
-    const masked = key.slice(0, 8) + "...";
-    stats[masked] = { count: record.count, month: record.monthKey };
+  if (apiKey) {
+    const record = usage.get(apiKey);
+    if (record) {
+      const masked = apiKey.slice(0, 8) + "...";
+      stats[masked] = { count: record.count, month: record.monthKey };
+    }
   }
   return stats;
 }

src/routes/billing.ts

@@ -74,7 +74,7 @@ a { color: #4f9; }
 <div class="card">
 <h1>🎉 Welcome to Pro!</h1>
 <p>Your API key:</p>
-<div class="key" onclick="navigator.clipboard.writeText('${escapeHtml(keyInfo.key)}')" title="Click to copy">${escapeHtml(keyInfo.key)}</div>
+<div class="key" style="position:relative">${escapeHtml(keyInfo.key)}<button onclick="navigator.clipboard.writeText('${escapeHtml(keyInfo.key)}');this.textContent='Copied!';setTimeout(()=>this.textContent='Copy',1500)" style="position:absolute;top:8px;right:8px;background:#4f9;color:#0a0a0a;border:none;border-radius:4px;padding:4px 12px;cursor:pointer;font-size:0.8rem;font-family:system-ui">Copy</button></div>
 <p><strong>Save this key!</strong> It won't be shown again.</p>
 <p>10,000 PDFs/month • All endpoints • Priority support</p>
 <p><a href="/docs">View API docs →</a></p>