Fix masternode registration: collateral check used wrong amount + empty obfuscation dummy address

Masternodes could never register on FairCoin v3 (every `masternode start-alias` was silently rejected with "mnb - Rejected Masternode entry"). Two bugs in the collateral validation:
- CheckInputsAndAdd / CMasternodeBroadcast built the collateral-check dummy tx with a hardcoded 9999.99 COIN output (a PIVX 10000-collateral leftover), but FairCoin's collateral is MASTER_NODE_AMOUNT = 5000. So AcceptableInputs/CheckInputs failed with "value in (5000) < value out (9999.99)". Fixed to 4999.99 (collateral minus 0.01 fee margin) in all three sites: src/masternode.cpp:214, src/masternode.cpp:575, src/masternodeman.cpp:962.
- strObfuscationPoolDummyAddress was "" (empty) in chainparams (mainnet), so CObfuscationPool::SetCollateralAddress logged "Invalid Obfuscation collateral address" and collateralPubKey stayed empty. Set it to a valid FairCoin address (used only to build the never-broadcast collateral-check tx).

Verified in production: with both fixes, `masternode start-alias` is accepted ("Got NEW Masternode entry"), the masternode shows status ENABLED across all nodes, and blocks pay the masternode 5 FAIR with SPORK_8 enforcement on.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: NateIsern

src/chainparams.cpp

@@ -434,7 +434,7 @@ class CMainParams : public CChainParams
 
         nPoolMaxTransactions = 3;
         strSporkKey = "044072106100b738bb99d24f2230708ebebdca687a01f8d0ce138551da829cf4e28ac499242806279787afc5293c97b72694f111e91c376cdb0d0fda8778ad4425";
-        strObfuscationPoolDummyAddress = "";
+        strObfuscationPoolDummyAddress = "FRZou2ApnnNyHGJRqoHgVLDF71Yviuhfz2"; // valid FairCoin addr; used only to build the collateral-check dummy tx (must be standard, never broadcast)
         nStartMasternodePayments = 1744156800; // April 9, 2026
     }
 

src/masternode.cpp

@@ -211,7 +211,7 @@ void CMasternode::Check(bool forceCheck)
     if (!unitTest) {
         CValidationState state;
         CMutableTransaction tx = CMutableTransaction();
-        CTxOut vout = CTxOut(9999.99 * COIN, obfuscationPool.collateralPubKey);
+        CTxOut vout = CTxOut(4999.99 * COIN, obfuscationPool.collateralPubKey); // MASTER_NODE_AMOUNT (5000) minus 0.01 fee margin
         tx.vin.push_back(vin);
         tx.vout.push_back(vout);
 
@@ -572,7 +572,7 @@ bool CMasternodeBroadcast::CheckInputsAndAdd(int& nDoS)
 
     CValidationState state;
     CMutableTransaction tx = CMutableTransaction();
-    CTxOut vout = CTxOut(9999.99 * COIN, obfuscationPool.collateralPubKey);
+    CTxOut vout = CTxOut(4999.99 * COIN, obfuscationPool.collateralPubKey); // MASTER_NODE_AMOUNT (5000) minus 0.01 fee margin
     tx.vin.push_back(vin);
     tx.vout.push_back(vout);
 

src/masternodeman.cpp

@@ -959,7 +959,7 @@ void CMasternodeMan::ProcessMessage(CNode* pfrom, std::string& strCommand, CData
 
         CValidationState state;
         CMutableTransaction tx = CMutableTransaction();
-        CTxOut vout = CTxOut(9999.99 * COIN, obfuscationPool.collateralPubKey);
+        CTxOut vout = CTxOut(4999.99 * COIN, obfuscationPool.collateralPubKey); // MASTER_NODE_AMOUNT (5000) minus 0.01 fee margin
         tx.vin.push_back(vin);
         tx.vout.push_back(vout);