feat: add TreeView SetAlign, SetTopLevel, SetGraphics, SetPrefixes config

[cassdeckard]

Summary

Add YAML configuration for TreeView's layout modes: SetAlign, SetTopLevel, SetGraphics, and SetPrefixes. These control how the tree is displayed (aligned, hidden root, line graphics, custom prefixes per level).

Background

Discovered while planning a tview presentation demo implementation via tviewyaml. The TreeView slide toggles between basic graphics, topLevel=1 (hide root), align mode, and custom prefixes.

Demo Usage

Layout modes not in TreeNode or primitive config.

Proposed Approach

• Add align: true/false, topLevel: 0|1|..., graphics: true/false, prefixes: ["prefix1", "prefix2", ...] to TreeView primitive config
• In populateTreeView, call SetAlign, SetTopLevel, SetGraphics, SetPrefixes when configured
• Prefixes support color tags (e.g. "[red]* ")

Relevant Files

• config/types.go – add TreeView layout fields to Primitive or PageConfig
• builder/builder.go – populateTreeView, buildTreeView
• docs/tview-coverage.md – document once implemented