refactor(console): phase 4b — extract ConsoleScrollController

Pull the auto-scroll concern out of ConsoleTab into a focused, ImGui-free
ConsoleScrollController (console_scroll_controller.{h,cpp}). It owns the three
coupled fields that were loose on the god-class — auto_scroll_, the wheel-up
cooldown, and the new-lines-while-scrolled-up backlog count — and the state
machine tying them together: wheel-up detaches + starts a cooldown, the cooldown
gates the at-bottom re-enable check, backlog counting happens only while
detached, and re-pinning (checkbox / jump pill / reaching the bottom) clears it.

The view keeps only what needs ImGui: it measures scroll position, hands the
controller a plain `atBottom` bool + frame delta, and issues the actual
SetScrollHereY. ConsoleTab loses three more members and all the scattered
auto-scroll bookkeeping collapses to scroll_.* calls.

Adds testConsoleScrollController: pinned start ignores backlog, wheel-up detach +
cooldown gating, re-enable only when at bottom, checkbox toggle semantics, and
the jump-to-bottom pill. Full-node + lite build clean; ctest green; source
hygiene clean.

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

src/ui/windows/console_tab.h

@@ -6,6 +6,7 @@
 
 #include "console_channel.h"
 #include "console_model.h"
+#include "console_scroll_controller.h"
 #include "console_selection_controller.h"
 #include "console_text_layout.h"
 #include "../layout.h"
@@ -117,11 +118,11 @@ private:
     std::vector<std::string> command_history_;
     int history_index_ = -1;
     char input_buffer_[4096] = {0};
-    bool auto_scroll_ = true;
-    float scroll_up_cooldown_ = 0.0f;    // seconds to wait before re-enabling auto-scroll
-    int  new_lines_since_scroll_ = 0;     // new lines while scrolled up (for indicator)
     // (log-ingestion cursors + result queue moved to the ConsoleCommandExecutor)
 
+    // Auto-scroll state machine (pin-to-bottom, wheel-up cooldown, new-line backlog count).
+    ConsoleScrollController scroll_;
+
     // Text-selection state + logic (anchor/caret, ordering, extraction, eviction shift).
     ConsoleSelectionController selection_;
     float output_scroll_y_ = 0.0f;    // Track scroll position for selection