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/rpcblockchain.cpp

@@ -128,7 +128,7 @@ Object blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool fPri
     result.push_back(Pair("modifier", strprintf("%016"PRIx64, blockindex->nStakeModifier)));
     result.push_back(Pair("modifierchecksum", strprintf("%08x", blockindex->nStakeModifierChecksum)));
     Array txinfo;
-    BOOST_FOREACH (const CTransaction& tx, block.vtx)
+    for (const CTransaction& tx : block.vtx)
     {
         if (fPrintTransactionDetail)
         {
@@ -211,7 +211,7 @@ Value getrawmempool(const Array& params, bool fHelp)
     mempool.queryHashes(vtxid);
 
     Array a;
-    BOOST_FOREACH(const uint256& hash, vtxid)
+    for (const uint256& hash : vtxid)
         a.push_back(hash.ToString());
 
     return a;