Fix fee calculation and improve token spendability detection

- Fix critical fee calculation bug: Now gets exact melt quote before creating invoice
- Improve spent token detection: Only marks as spent with clear indicators
- Add spent field to decode endpoint response (always boolean)
- Add informative root endpoint with API documentation
- Update documentation examples to use cashuB format
- Install bolt11 library for proper Lightning invoice verification
- Enhanced error handling and logging throughout

This fixes the issue where users lost sats due to fee estimation errors
and ensures accurate token spendability detection.

package.json

@@ -26,6 +26,7 @@
   "dependencies": {
     "@cashu/cashu-ts": "^1.1.0",
     "axios": "^1.7.7",
+    "bolt11": "^1.4.1",
     "cors": "^2.8.5",
     "dotenv": "^16.4.5",
     "express": "^4.19.2",
@@ -34,8 +35,8 @@
     "uuid": "^10.0.0"
   },
   "devDependencies": {
-    "nodemon": "^3.1.4",
-    "eslint": "^9.9.1"
+    "eslint": "^9.9.1",
+    "nodemon": "^3.1.4"
   },
   "engines": {
     "node": ">=18.0.0",