fix(gui): stop Reset Fields wiping the search history, gate the history UI - #709

Summary

Closes #697. Four fixes around the search Name field, addressing all three of @ghysler's proposals plus a crash found while auditing the call sites.

1. "Reset Fields" wiped the whole search history

The reported bug, and the cause is a subtle one. The call already cast to wxTextEntry specifically to avoid this, with a comment saying so — but the cast doesn't help:

// wxComboBoxBase, include/wx/combobox.h
virtual void Clear() override
{
    wxItemContainer::Clear();   // ← the dropdown's item list
    wxTextEntry::Clear();
}

wxTextEntry::Clear() is virtual, so calling it through a wxTextEntry* dispatches to the combo override and empties the item list too. Now uses SetValue(""), which only touches the text.

This also explains the second half of the report — the last term still being offered as a completion after the pull-down looked empty. The item list was being cleared while the autocomplete set stayed armed, so proposal (3) resolves with the same fix rather than needing its own.

2. Crash in "search related files"

SearchListCtrl.cpp did CastByID(IDC_SEARCHNAME, …, wxTextCtrl)->SetValue(keyword). The field became a wxComboBox in #643, and wxComboBox doesn't derive from wxTextCtrl — it's wxWindowWithItems<wxControl, wxComboBoxBase>. CastByID is a dynamic_cast, so that yielded nullptr and the SetValue() dereferenced it. Reachable whenever you're connected to an ed2k server. Cast to wxTextEntry, the common base.

3. "Clear search history" as a visible button

Proposal (2). The action already existed in the field's right-click menu, but that menu is unreachable on Windows: the editable part of a wxComboBox is a native child EDIT window, and per ShouldForwardFromEditToCombo() in src/msw/combobox.cpp wx forwards only WM_KEYUP/KEYDOWN/CHAR/SYSCHAR/SYSKEYDOWN/SYSKEYUP/SETFOCUS/KILLFOCUS/CUT/COPY/PASTE from it. WM_CONTEXTMENU isn't among them, so the native menu appears and our handler never runs — matching @ghysler's screenshot exactly.

The button sits after the search-type choice and greys out when there's nothing stored. Built in SearchDlg.cpp rather than muuli_wdr.cpp so the existing msgid keeps its catalog position — adding the same string to muuli_wdr.cpp would move the pot entry, since xgettext orders entries by file scan order, and that trips pot-sync. No catalog changes in this PR.

4. The preference now gates the whole history UI

"Remember search history" previously only stopped new terms being recorded: existing terms stayed in the dropdown, kept being offered as completions, and the field kept its dropdown regardless. Now, with it off, the Name field is a plain wxTextCtrl, the Clear button is hidden, and no stored terms are loaded. searchhistory.dat is deliberately left on disk, so re-enabling restores the previous history rather than starting over.

Applied live from PrefsUnifiedDlg::OnOk via CfgChanged(IDC_SEARCHHISTORYENABLED), following the same idiom as the existing IDC_EXTCATINFO / IDC_SLIDER branches, so no restart is needed. The swap uses wxSizer::Replace, carries the typed value across, keeps wxTE_PROCESS_ENTER so Enter still searches, and re-binds the context menu when a combo is created.

Testing

Built monolithic + amulegui clean on macOS ARM64, Ubuntu ARM64 (wxGTK3) and Windows ARM64. git clang-format origin/master clean; diff-scoped Tier-2 clang-tidy clean. Verified on the Windows portable: the crash is gone, Reset Fields keeps the dropdown, and the preference toggle swaps the field and the button live in both directions.