Improve peer connectivity, UI responsiveness, and add auto-bootstrap

Peer connectivity (small network optimizations):
- Reduce hardcoded seed fallback delay from 30s to 10s
- Reduce peer retry interval from 600s to 120s
- Lower staking minimum peers from 3 to 1
- Relay addr messages to all connected peers instead of just 2

UI responsiveness:
- Add progress reporting to ScanForWalletTransactions (every 10K blocks)
- Use TRY_LOCK in WalletModel::pollBalanceChanged to avoid blocking UI
- Use TRY_LOCK in TransactionTablePriv::refreshWallet with retry

Auto-bootstrap:
- Add bootstrap.h/cpp with HTTP download via boost::asio
- On first run, prompt user to download blockchain snapshot from
  bootstrap.cryptographic-triangles.org directly into data directory
- Downloads filelist.txt manifest then each file with progress dialog
- Falls back to IP 194.233.88.206 if DNS fails
- Gracefully continues to P2P sync if bootstrap unavailable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/qt/transactiontablemodel.cpp

@@ -71,7 +71,13 @@ public:
         OutputDebugStringF("refreshWallet\n");
         cachedWallet.clear();
         {
-            LOCK(wallet->cs_wallet);
+            TRY_LOCK(wallet->cs_wallet, lockWallet);
+            if(!lockWallet)
+            {
+                // Lock busy (block processing), retry in 500ms
+                QTimer::singleShot(500, parent, SLOT(refreshWallet()));
+                return;
+            }
             for(std::map<uint256, CWalletTx>::iterator it = wallet->mapWallet.begin(); it != wallet->mapWallet.end(); ++it)
             {
                 if(TransactionRecord::showTransaction(it->second))