perf: stop per-frame SQLite writes and console spam, make perf.log opt-in

- Explorer: the tip check runs every frame the Explorer tab is open,
  and it read both tip rows and rewrote them each time (two autocommit
  WAL writes per frame). A steady tip is now kept in memory and skips
  SQLite. A new tip writes both rows in one savepoint, so a crash
  between them can't pair a new height with the old hash. A test
  checks that 100 steady checks write nothing.
- Console: while the daemon was in the Error state the Console tab
  added its error line on every poll, i.e. every frame, re-laying out
  the whole buffer each time. It prints once per error now: on entering
  Error, when the message changes, or after another crash
  (EmbeddedDaemon::getUnexpectedExitCount(), never reset). setState
  writes the message before the state, so a reader that sees Error sees
  that error's message. The stray " ===" suffix is gone.
- perf.log: the profiler appended a block every 300 frames on every
  run and never rotated the file (tens of MB a day for a wallet left
  open). It is now off unless the app starts with DRAGONX_PERFLOG=1;
  otherwise its zone hooks are near no-ops.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.cpp

@@ -77,6 +77,7 @@ extern "C" HRESULT __stdcall SHGetPropertyStoreForWindow(HWND hwnd, REFIID riid,
 #include <cstdlib>
 #include <cmath>
 #include <cstdint>
+#include <cstring>
 #include <filesystem>
 #include <fstream>
 #include <string>
@@ -1447,8 +1448,10 @@ int main(int argc, char* argv[])
         dragonx::ui::schema::UISchema::instance().reapplyColorsToImGui();
     }
 
-    // Initialize performance profiler — writes to <ObsidianDragonDir>/perf.log
-    {
+    // Performance profiler — writes to <ObsidianDragonDir>/perf.log. Opt-in (DRAGONX_PERFLOG=1): always
+    // on, it appended a block every 300 frames and was never rotated (tens of MB a day for any wallet
+    // left open).
+    if (const char* perfEnv = std::getenv("DRAGONX_PERFLOG"); perfEnv && *perfEnv && std::strcmp(perfEnv, "0") != 0) {
         std::string perfPath = (std::filesystem::path(
             dragonx::util::Platform::getObsidianDragonDir()) / "perf.log").string();
         dragonx::util::PerfLog::instance().init(perfPath);