feat(console): collapsible JSON in command output

Add fold/unfold of JSON objects and arrays in console command results, built on
the refactored channel + model foundation.

- ComputeConsoleFoldSpans() (console_input_model): pure brace/bracket matcher
  over a block of pretty-printed JSON lines; each opener line gets the offset to
  its matching closer at the same indentation (empty/one-line blocks are not
  foldable). Unit tested (nested objects, arrays, empty blocks, non-JSON, and a
  string value that merely contains a brace).
- ConsoleModelLine gains foldSpan (relative, so it survives front-eviction by the
  line cap) + a collapsed flag; ingest() carries the span and toggleCollapsed()
  flips openers (main thread). addFormattedResult computes the block's spans and
  ingests them atomically.
- computeVisibleLines() skips a collapsed block's interior (opener stays, its
  foldSpan lines through the closer are hidden); folding is bypassed while a
  filter is active so every match stays reachable.
- drawVisibleLines() draws a fold triangle in the free left gutter of opener
  lines (result/JSON channels carry no accent bar there), toggled by a click in
  the gutter cell, and appends a dim " ... }" / " ... ]" summary on collapsed
  openers.

Full-node + lite build clean; ctest green (incl. fold-span + model-fold tests);
source hygiene clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/console_model.cpp

@@ -9,10 +9,14 @@
 namespace dragonx {
 namespace ui {
 
-void ConsoleModel::ingest(const std::string& text, ConsoleChannel channel)
+void ConsoleModel::ingest(const std::string& text, ConsoleChannel channel, int foldSpan)
 {
     std::lock_guard<std::mutex> lock(ingest_mutex_);
-    pending_.push_back({text, channel});
+    ConsoleModelLine line;
+    line.text = text;
+    line.channel = channel;
+    line.foldSpan = foldSpan;
+    pending_.push_back(std::move(line));
 }
 
 ConsoleModel::DrainResult ConsoleModel::drain()
@@ -41,5 +45,12 @@ void ConsoleModel::clear()
     lines_.clear();
 }
 
+bool ConsoleModel::toggleCollapsed(std::size_t i)
+{
+    if (i >= lines_.size() || lines_[i].foldSpan <= 0) return false;
+    lines_[i].collapsed = !lines_[i].collapsed;
+    return lines_[i].collapsed;
+}
+
 } // namespace ui
 } // namespace dragonx