#817: TUI runs two double-click detectors — adopt quadraui DoubleClickDetector and delete the hand-rolled 400ms window - #844

… timer

mouse::handle_mouse ran a second, independent 400ms/position double-click
detector (last_click_time/last_click_pos) at five sites, racing the
DoubleClickDetector TuiBackend already runs to produce the UiEvent::DoubleClick
that reaches TuiShellApp::handle_mouse_event. Replace the hand-rolled state
with a single `is_double_click: bool` parameter captured from the real
UiEvent::DoubleClick before it's folded to a crossterm MouseEvent, and read it
directly at all five sites (find/replace input, ext panel row, git/sc sidebar
row, settings row, editor word-select) instead of re-deriving it.

Net effect: handle_mouse drops from 33 to 32 parameters (one hand-rolled
timer's worth), and the two detectors that could disagree collapse into one.

GTK already routes UiEvent::DoubleClick straight to its handlers with no
duplicate detector — no change needed there.

Adds two black-box regression tests via TuiDriver: double-click word
selection in the editor (using TuiDriver::double_click, quadraui#592's
deterministic non-wall-clock double-click event) and double-click toggling a
boolean settings row. Both were verified red against the pre-fix behavior
(is_double hardcoded false) and green with the fix.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

…nd SC-sidebar sites

The review flagged that the original fix removed the hand-rolled 400ms
detector at all five mouse.rs call sites but only added regression tests
for two (editor word-select, settings toggle). Add the two the issue's
Acceptance section names explicitly:

- tui_ext_panel_double_click_on_a_section_header_does_not_toggle_it:
  double-clicking an extension-panel section header must not toggle its
  expand/collapse state (handle_ext_panel_double_click no-ops on header
  rows; the single-click Return toggle must be suppressed).
- tui_sc_sidebar_double_click_on_a_changed_file_opens_it: double-clicking
  a changed file's row in the source-control sidebar must open it via
  sc_activate_row, same as double-clicking a file in the Explorer.

Both use TuiDriver::double_click to deliver a single synthetic
UiEvent::DoubleClick with no preceding click, and both were verified RED
(by temporarily hardcoding each arm's is_double to false) against the
behavior the deleted hand-rolled detector would have produced for a lone
injected event: no prior last_click_time to compare against, so it would
have read as an ordinary first click.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>