Modernize codebase: C++17, remove Tor v2, add embedded Tor scaffold, IBD speedups

- Replace ~290 BOOST_FOREACH with C++11 range-for across 41+ files
- Replace boost::assign::map_list_of with C++11 brace initialization
- Remove PAIRTYPE macro (no longer needed without BOOST_FOREACH)
- Guard OpenSSL locking callbacks for 3.x (no-ops in >= 1.1.0)
- Fix Qt deprecated APIs for Qt6 compat (QStyleOptionViewItemV4, setResizeMode)
- Add openssl_compat.h version string wrapper
- Enable C++17 in makefile.unix and triangles-qt.pro

- Delete 163 dead Tor v2 source files (~150K lines removed)
- Add embedded Tor scaffold (tor_embedded.h/cpp) using tor_api.h
- Add build-libtor.sh helper and CODEX-TOR-GUIDE.md
- Update makefile.unix and .pro with USE_TOR_EMBEDDED optional flag
- Fallback to external tor_process when not compiled with libtor

- IBD pipeline refill: 100 -> 1000 blocks
- Send/recv buffer limits: unlimited -> 100MB/32MB
- Orphan block cap: unlimited -> 750 with random eviction
- Socket poll: 10ms -> 1ms during IBD
- Message handler sleep: 10ms -> 1ms during IBD
- Stall detection timeout: 5s -> 2s

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

src/txdb-leveldb.cpp

@@ -432,7 +432,7 @@ bool CTxDB::LoadBlockIndex()
     // Calculate nChainTrust
     vector<pair<int, CBlockIndex*> > vSortedByHeight;
     vSortedByHeight.reserve(mapBlockIndex.size());
-    BOOST_FOREACH(const PAIRTYPE(uint256, CBlockIndex*)& item, mapBlockIndex)
+    for (const auto& item : mapBlockIndex)
     {
         CBlockIndex* pindex = item.second;
         vSortedByHeight.push_back(make_pair(pindex->nHeight, pindex));
@@ -443,7 +443,7 @@ bool CTxDB::LoadBlockIndex()
     int nProgressInterval = std::max((int)vSortedByHeight.size() / 20, 1);
     int nCount = 0;
 
-    BOOST_FOREACH(const PAIRTYPE(int, CBlockIndex*)& item, vSortedByHeight)
+    for (const auto& item : vSortedByHeight)
     {
         CBlockIndex* pindex = item.second;
         pindex->nChainTrust = (pindex->pprev ? pindex->pprev->nChainTrust : 0) + pindex->GetBlockTrust();
@@ -530,7 +530,7 @@ bool CTxDB::LoadBlockIndex()
         {
             pair<unsigned int, unsigned int> pos = make_pair(pindex->nFile, pindex->nBlockPos);
             mapBlockPos[pos] = pindex;
-            BOOST_FOREACH(const CTransaction &tx, block.vtx)
+            for (const CTransaction &tx : block.vtx)
             {
                 uint256 hashTx = tx.GetHash();
                 CTxIndex txindex;
@@ -557,7 +557,7 @@ bool CTxDB::LoadBlockIndex()
                     unsigned int nOutput = 0;
                     if (nCheckLevel>3)
                     {
-                        BOOST_FOREACH(const CDiskTxPos &txpos, txindex.vSpent)
+                        for (const CDiskTxPos &txpos : txindex.vSpent)
                         {
                             if (!txpos.IsNull())
                             {
@@ -584,7 +584,7 @@ bool CTxDB::LoadBlockIndex()
                                     else
                                     {
                                         bool fFound = false;
-                                        BOOST_FOREACH(const CTxIn &txin, txSpend.vin)
+                                        for (const CTxIn &txin : txSpend.vin)
                                             if (txin.prevout.hash == hashTx && txin.prevout.n == nOutput)
                                                 fFound = true;
                                         if (!fFound)
@@ -602,7 +602,7 @@ bool CTxDB::LoadBlockIndex()
                 // check level 5: check whether all prevouts are marked spent
                 if (nCheckLevel>4)
                 {
-                     BOOST_FOREACH(const CTxIn &txin, tx.vin)
+                     for (const CTxIn &txin : tx.vin)
                      {
                           CTxIndex txindex;
                           if (ReadTxIndex(txin.prevout.hash, txindex))