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/sync.cpp

@@ -5,7 +5,6 @@
 #include "sync.h"
 #include "util.h"
 
-#include <boost/foreach.hpp>
 
 #ifdef DEBUG_LOCKCONTENTION
 void PrintLockContention(const char* pszName, const char* pszFile, int nLine)
@@ -58,14 +57,14 @@ static void potential_deadlock_detected(const std::pair<void*, void*>& mismatch,
 {
     printf("POTENTIAL DEADLOCK DETECTED\n");
     printf("Previous lock order was:\n");
-    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s2)
+    for (const auto& i : s2)
     {
         if (i.first == mismatch.first) printf(" (1)");
         if (i.first == mismatch.second) printf(" (2)");
         printf(" %s\n", i.second.ToString().c_str());
     }
     printf("Current lock order is:\n");
-    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s1)
+    for (const auto& i : s1)
     {
         if (i.first == mismatch.first) printf(" (1)");
         if (i.first == mismatch.second) printf(" (2)");
@@ -84,7 +83,7 @@ static void push_lock(void* c, const CLockLocation& locklocation, bool fTry)
     (*lockstack).push_back(std::make_pair(c, locklocation));
 
     if (!fTry) {
-        BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, (*lockstack)) {
+        for (const auto& i : (*lockstack)) {
             if (i.first == c) break;
 
             std::pair<void*, void*> p1 = std::make_pair(i.first, c);