refactor(console): phase 1 — extract pure ConsoleTextLayout (wrap/hit-test/selection)

Lift the console's word-wrap layout, screen->text hit-testing, and selection extraction
out of ConsoleTab into a pure, ImGui-free module (console_text_layout.{h,cpp}). Text
measurement is injected via a ConsoleTextMeasure interface — production uses an
ImFont-backed impl (identical CalcWordWrapPositionA/CalcTextSizeA calls as before), while
tests drive a fixed-width stub.

- BuildConsoleLayout: per-line wrap segments + heights + cumulative Y (was inline in
  renderOutput).
- HitTestConsoleLayout: point -> (visibleRow, byte col) (was screenToTextPos).
- ExtractConsoleSelection: selected text across visible lines (was getSelectedText).
- ConsoleTab now holds a single `ConsoleLayout layout_` (replacing 4 mutable members;
  drops the dead cached_wrap_width_) and calls the pure functions.
- New unit test testConsoleTextLayout covers wrapping, multi-row hit-testing, bottom
  clamp, and filtered/unfiltered selection — the biggest previously-untested surface.

No behavior change (algorithm preserved verbatim). Full-node + lite build clean, ctest
green.

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

CMakeLists.txt

@@ -460,6 +460,7 @@ set(APP_SOURCES
     src/ui/windows/console_input_model.cpp
     src/ui/windows/console_output_model.cpp
     src/ui/windows/console_tab_helpers.cpp
+    src/ui/windows/console_text_layout.cpp
     src/ui/windows/settings_window.cpp
     src/ui/pages/settings_page.cpp
     src/ui/windows/about_dialog.cpp
@@ -1019,6 +1020,7 @@ if(BUILD_TESTING)
         src/ui/windows/console_input_model.cpp
         src/ui/windows/console_output_model.cpp
         src/ui/windows/console_tab_helpers.cpp
+        src/ui/windows/console_text_layout.cpp
         src/ui/windows/mining_benchmark.cpp
         src/ui/windows/mining_pool_panel.cpp
         src/ui/windows/mining_tab_helpers.cpp