Fix rate limits, concurrency control, copy button

- DATA-BACKED RATE LIMITS:
  * Reduce global rate limit from 10,000/min to 100/min
  * Add PDF conversion rate limits: 10/min free, 30/min pro
  * Set recovery rate limit to 3/hour (was 5/hour)
  * Add concurrency limiter: max 3 simultaneous PDFs, queue rest
  * Return 429 if queue > 10

- BUG-025: Fix copy button functionality
  * Improve fallback handling for execCommand
  * Add better error handling and user feedback
  * Fix secure context detection

- Add concurrency monitoring endpoint /v1/concurrency

state.json

@@ -0,0 +1,35 @@
+{
+  "project": "DocFast",
+  "domain": "docfast.dev",
+  "server": "167.235.156.214",
+  "sshKey": "/home/openclaw/.ssh/docfast",
+  "repo": "openclawd/docfast",
+  "status": "live",
+  "version": "0.2.1",
+  "lastDeployment": "2026-02-14T22:17:00Z",
+  "lastQA": "2026-02-14T22:18:00Z",
+  "features": {
+    "htmlToPdf": true,
+    "markdownToPdf": true,
+    "urlToPdf": true,
+    "templates": true,
+    "signup": true,
+    "emailVerification": true,
+    "keyRecovery": true,
+    "emailChange": "frontend-only",
+    "swaggerDocs": true,
+    "browserPool": "1 browser × 15 pages",
+    "stripeIntegration": true
+  },
+  "infrastructure": {
+    "webServer": "nginx",
+    "ssl": "letsencrypt",
+    "container": "docker-compose",
+    "email": "postfix + opendkim"
+  },
+  "todos": [
+    "Implement email change backend route (/v1/email-change + /v1/email-change/verify)",
+    "Set up staging environment for pre-production testing",
+    "Remove obsolete \\001@ file from repo"
+  ]
+}