Fix autocomplete popup focus handling

[Lili889-ods]

Brief overview of PR changes/additions

Fixes autocomplete popup focus handling in TextEditorAutoCompleteComponent.

The autocomplete popup and its internal QListWidget are kept non-focusable and shown without activating. When autocomplete is visible, editor key events route only the autocomplete-specific commands to the list:

• Up/Down/PageUp/PageDown move through suggestions.
• Enter/Return/Tab accept the current suggestion.
• Escape closes autocomplete.
• Normal typing and Backspace stay with the editor.

A regression test covers that showing autocomplete keeps focus on the editor and that keyboard selection still works.

Motivation for adding to Mudlet

Mudlet issue #5310 reports that Lua autocomplete can steal focus and prevent continued typing. The root cause is that autocomplete currently calls listWidgetRef_->setFocus() after showing suggestions.

Other info (issues closed, discussion etc)

Related Mudlet issue: Mudlet/Mudlet#5310

Testing:

• cmake -S 3rdparty/edbee-lib -B /private/tmp/mudlet-edbee-build -DCMAKE_BUILD_TYPE=Debug -DBUILD_WITH_QT5=OFF
• cmake --build /private/tmp/mudlet-edbee-build --target edbee-lib -j4
• git -C 3rdparty/edbee-lib diff --check

The new test source compiles, but I could not link/run the full local edbee-test executable on this macOS machine because the Qt test executable link step fails with ld: framework 'AGL' not found, unrelated to this change.