fix: a zero-width band fires on equality, not never; dead accessors removed

- The comment in `feed_window()` and three companion sites claimed a zero-width band
  "never fires, because no sample can be on a different side of it than its neighbour".
  That is false: `inside = value >= lo && value <= hi` with `lo == hi == 1.0` is true at
  +1 and false at -1, so a ±1 square fires 19 times in 20 samples.  The correct reason
  the panel refuses one is that it reduces the condition to a float-equality test on a
  real-valued signal, which in practice never fires (fix 4).
- `EventDetector::condition()`, `BufferSearch::channel()` and `BufferSearch::condition_`
  were confirmed unused by grep and deleted (fix 10).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/search.hpp

@@ -57,7 +57,6 @@ class BufferSearch {
   bool pump(ScopeModel& model);
 
   State state() const noexcept { return state_; }
-  int channel() const noexcept { return channel_; }
   const std::vector<double>& hits() const noexcept { return hits_; }
   /// Which hit the view is on, or -1 for none.
   int cursor() const noexcept { return cursor_; }
@@ -77,7 +76,6 @@ class BufferSearch {
 
  private:
   EventDetector detector_{};
-  EventCondition condition_{};
   int channel_ = -1;
   State state_ = State::Idle;
   bool started_ = false;       ///< the index range has been established.