Fixes #5365. Fix Markdown auto-focus, Home/End keys, and Deepdives Tab nav

[tig]

Summary

Four fixes for the Markdown view and Deepdives scenario:

1. Fix Markdown auto-focuses last link on initial render (#5365)

Root cause: MarkdownTable.BuildLinkRegions() set CanFocus = true before the table was added via Add(). View.AddAt() auto-focuses any focusable subview when the SuperView has focus — so each successive table stole focus, leaving the last one focused and scrolling the viewport to the bottom.

Fix: Removed CanFocus assignment from BuildLinkRegions(). Instead, Markdown.OnSubViewLayout() manages table focusability after all Add() calls complete, then clears any auto-focused table to keep the viewport at the top.

2. Add Home/End key support to Markdown

Home/End keys now scroll to the top/bottom of the document (same as Ctrl+Home/End which were already bound). Markdown is a read-only view with no cursor, so plain Home/End should behave identically to Ctrl+Home/End.

3. Fix Deepdives Tab navigation

FrameView defaults to TabBehavior.TabGroup, which means Tab cycles within the frame and F6/Ctrl+Tab is required to move between frames. Set both FrameViews to TabBehavior.TabStop so Tab naturally navigates between the doc list and markdown viewer.

4. Prevent CursorDown/Up from escaping Docs list

When the ListView reaches the bottom/top of the list and CursorDown/Up is unhandled, it propagates to the Application level where it's aliased to NextTabStop, shifting focus to the markdown viewer. Added KeyDownNotHandled handler on the list to consume arrow keys at boundaries.

Testing

• Added regression test: Initial_Render_With_Table_Links_Does_Not_Scroll_Viewport
• All 93 MarkdownView + 38 MarkdownTable tests pass

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[Copilot]

Pull request overview

This PR targets Markdown view navigation/focus behavior (including a regression for #5365), adds Home/End scrolling support for Markdown, and adjusts the UICatalog “Deepdives” scenario’s tab navigation.

Changes:

• Add Markdown commands so Home/End (without Ctrl) scroll to top/bottom like Ctrl+Home/End.
• Attempt to prevent initial auto-focus/auto-scroll behavior involving Markdown tables/links, and add a regression test for #5365.
• Change Deepdives scenario FrameViews to TabBehavior.TabStop to make Tab move between panes.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Tests/UnitTestsParallelizable/Views/Markdown/MarkdownViewTests.cs	Adds regression test for initial render viewport position/focus with table links.
Terminal.Gui/Views/Markdown/MarkdownView.Mouse.cs	Adds Home/End command handlers and changes focus-advance behavior when focus is gained.
Terminal.Gui/Views/Markdown/MarkdownTable.cs	Adds HasLinks and updates link-region focusability logic/comments.
Terminal.Gui/Views/Markdown/Markdown.cs	Adds logic in layout to clear table auto-focus after rebuilding subviews.
Examples/UICatalog/Scenarios/Deepdives.cs	Sets both FrameViews to TabBehavior.TabStop to change Tab traversal behavior.

Comments suppressed due to low confidence (1)

Examples/UICatalog/Scenarios/Deepdives.cs:54

• PR description mentions consuming CursorUp/Down at ListView boundaries (KeyDownNotHandled) to prevent focus from jumping to the markdown viewer, but this scenario code only changes TabStop on the frames. If that arrow-key boundary handling is still required, it looks missing here and should be added to _docList to match the described behavior.

        FrameView listFrame = new ()
        {
            Title = "_Docs",
            X = 0,
            Y = 0,
            Width = 30,
            Height = Dim.Fill (1),
            TabStop = TabBehavior.TabStop
        };

        _docList = new ListView { Width = Dim.Fill (), Height = Dim.Fill () };

        _docList.ValueChanged += OnDocListValueChanged;
        listFrame.Add (_docList);