Improve input handling and scrolling behavior for high-resolution trackpads.

- Added precise fractional mouse wheel delta handling with per-step command emission.
- Introduced scroll accumulators (`wheel_accum_y_`, `wheel_accum_x_`) for high-resolution trackpad input.
- Replaced hardcoded ESC delay with configurable `kEscDelayMs` constant in `TerminalFrontend`.
- Enabled mouse position reporting and reduced CPU usage during idle with optimized `timeout()` setting.

ImGuiInputHandler.h

@@ -41,4 +41,9 @@ private:
 	bool suppress_text_input_once_ = false;
 
 	Editor *ed_ = nullptr; // attached editor for editor-owned uarg handling
+
+	// Accumulators for high-resolution (trackpad) scrolling. We emit one scroll
+	// command per whole step and keep the fractional remainder.
+	float wheel_accum_y_ = 0.0f;
+	float wheel_accum_x_ = 0.0f; // reserved for future horizontal scrolling
 };