Keep autocomplete from stealing editor focus

[apples-kksk]

Addresses Mudlet/Mudlet#5310.
/claim Mudlet/Mudlet#5310

Summary:

• keep the editor component as the focused widget while autocomplete is visible
• make the autocomplete menu/list non-focus widgets and avoid activating the popup window
• route editor-origin navigation keys to the autocomplete list, while normal typing/backspace continues through the editor
• preserve legacy popup/list key handling with a recursion guard for forwarded events
• avoid calling editorComponentRef_->setFocus() on close, so autocomplete does not reclaim focus from another non-edbee widget
• add focused regression tests for editor focus, list-origin key forwarding, arrow navigation, completion acceptance, full-word Enter fall-through, Escape cancellation, and external-widget focus preservation

This is intentionally different from #11: it removes the known focus-grabbing path instead of restoring editor focus after the popup closes. It is similar in implementation direction to #12, but adds broader coverage for the focus and key-routing behavior.

Proof:

The proof GIF is generated from the actual edbee widget. It shows autocomplete opening without list focus, Down arrow changing the list selection, typing continuing into the editor, list-origin text keys routing back to the editor, Escape closing autocomplete, and closing autocomplete without stealing focus from another widget.

Verification:

• git diff --check
• cmake -S . -B build/codex-qt6 -DCMAKE_BUILD_TYPE=Debug
• cmake --build build/codex-qt6 --parallel 6
• QT_FORCE_STDERR_LOGGING=1 QT_MESSAGE_PATTERN='%{message}' QT_QPA_PLATFORM=offscreen ./build/codex-qt6/edbee-test/edbee-test (815 passed, 0 failures)

Follow-up:

• after this lands, Mudlet/Mudlet still needs a submodule-pointer PR for 3rdparty/edbee-lib so Mudlet builds include the edbee-lib fix.