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/ui/windows/console_command_executor.h

@@ -110,6 +110,8 @@ private:
     size_t last_daemon_output_size_ = 0;
     size_t last_xmrig_output_size_  = 0;
     int    last_daemon_state_       = -1;  // daemon::EmbeddedDaemon::State as int
+    std::string last_daemon_error_;         // error text last printed (main thread only)
+    std::uint64_t last_printed_exit_count_ = 0;   // daemon unexpected-exit count at that print
     bool   last_rpc_connected_      = false;
     std::deque<std::pair<std::string, bool>> results_;  // {text, isError}
     std::mutex results_mutex_;