fix(gui): give the log panes a text margin so text isn't flush to the frame - #707

Summary

Addresses #702. The log and Server Info panes render their text hard against the control's frame, with no padding at all — most obvious on themes that draw a tight, high-contrast border, which is how it was reported on Debian/MATE.

Root cause

Not a theme issue, and not Linux-specific. CMuleLogCtrl is a wxStyledTextCtrl, and its constructor zeroes Scintilla's three numbered margins so the pane reads as a plain log rather than a code editor:

for (int margin = 0; margin < 3; ++margin) {
    SetMarginWidth(margin, 0);
}

Those gutters were the only inset the control had, so removing them left the text starting at x=0. Scintilla draws its own text area, so this happens identically on every platform — it just reads as fine on Adwaita, macOS and Windows, where the frame is softer or slightly inset, and jumps out on a tighter border.

Fix

Horizontally, set the text-area margins, which are a distinct concept from the numbered margins, so the code-editor gutters stay gone:

const int textMargin = FromDIP(5);
SetMarginLeft(textMargin);
SetMarginRight(textMargin);

Scintilla's own default here is 1px (ViewStyle::Init), which is what made the text look flush — so the value has to be visibly above the default rather than a nudge past it.

Vertically, Scintilla has no counterpart to those margins, so the first line otherwise sits directly on the frame. extraAscent is the only vertical knob, and it feeds lineHeight (ViewStyle::Refresh: maxAscent += extraAscent), so it is line spacing rather than a one-off top gap:

SetExtraAscent(FromDIP(2));

That is the better fit here rather than a limitation worked around: the log tails to the bottom, so a fixed band at the viewport top would only ever appear above a partially scrolled line, whereas uniform spacing reads correctly both when the content scrolls and when it is short enough not to.

Both values are DIP-scaled so the gaps hold their size on HiDPI.

Tail-scroll is unaffected

Worth stating explicitly, since extraAscent changes lineHeight: the auto-scroll path reasons in display lines and never in pixels. AtBottom() compares GetFirstVisibleLine() + LinesOnScreen() against the display-line count, and OnInternalIdle() only compares GetFirstVisibleLine() values. Scintilla derives LinesOnScreen() from the same lineHeight it lays out with, so both sides of the comparison move together, and the existing - 1 slack in AtBottom() already absorbs partial-row rounding. The batch replay path (m_batchTailing) inherits the same reasoning.

Scope

Covers all three CMuleLogCtrl panes: aMule Log, Server Info, and amulegui's aMuleGUI Log.

The ED2K Info and Kad Info panes in the same notebook are native two-column wxListCtrls, not Scintilla, so they're untouched by this. Their cell padding comes from the platform theme and wxListCtrl offers no portable equivalent, so if they need the same treatment it's a separate change — either a GTK-only style tweak or converting those panes to CMuleLogCtrl like the other two already are. Deliberately not using a closing keyword for #702 so the issue stays open pending @mifritscher2's word on whether the Info lists still look wrong.

Testing

Built monolithic clean on macOS ARM64 and Ubuntu ARM64 (wxGTK3), and checked visually on both. git clang-format origin/master reports no deviation, and the diff-scoped Tier-2 clang-tidy run is clean with zero compiler errors. The previous horizontal-only revision passed all 14 CI checks.