fix(daemon): reset the console offset to the watermark on restart

When the daemon was restarted, the output-parse offset was reset to 0.
The daemon's output buffer is retained across runs, so the next poll
re-read the whole retained tail of the previous run and fed it to the
busy tracker as if it were fresh. A witness rebuild or rescan line left
over from the old run could then be mistaken for activity in the new
one.

- On restart the offset is now reset to the absolute end of the output
  at that moment, captured on the lifecycle thread after the stop and
  before the start, so the UI resumes parsing only the new run's output
  rather than replaying the old tail.
- The capture is handed to the UI thread through a pending flag and
  applied there before the next read, both on the normal poll and when
  skipping the backlog, so the offset is only ever moved on the thread
  that owns it.

Tests cover reading from the captured watermark (only the new run is
seen) versus the old reset-to-0 behaviour (the previous run replays).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.h

@@ -569,6 +569,7 @@ public:
     // output parser skips while the wallet is locked), so a background witness rebuild that started and
     // finished meanwhile isn't parsed in one batch and mistaken for a completed rescan (spurious toast).
     void skipDaemonOutputBacklog();
+    void applyPendingDaemonOutputReset();
     // A real user input event (key, text, mouse, touch, pen, gamepad button) was ingested. Main thread only.
     // Called from main.cpp's noteEvent; do NOT call from an SDL event watch/filter (resizeWatcher).
     void noteUserInput() { idle_.noteActivity(); }
@@ -1452,6 +1453,8 @@ private:
     void setDaemonStatus(std::string s);
     mutable std::string daemon_mem_diag_;  // diagnostic info for daemon memory detection
     size_t daemon_output_offset_ = 0;      // for incremental output parsing (rescan detection)
+    std::atomic<bool>   daemon_output_reset_pending_{false};   // lifecycle thread -> UI thread
+    std::atomic<size_t> daemon_output_reset_to_{0};
     // What the node's own output says it is doing (witness rebuild / startup replay). Fed on the UI thread
     // from the captured output; node_rebuilding_ is its snapshot for the shutdown thread's stop loop.
     daemon::DaemonBusyTracker daemon_busy_;