feat: add TableCell SetExpansion and NotSelectable config

[cassdeckard]

Summary

Add per-cell configuration for TableCell's SetExpansion and NotSelectable so individual cells can control expansion and selectability. Currently table config only supports row-level styling.

Background

Discovered while planning a tview presentation demo implementation via tviewyaml. The Table slide uses SetExpansion(1) on certain columns and NotSelectable for header/first-column cells.

Demo Usage

Per-cell expansion and NotSelectable; not in config.

Proposed Approach

• Extend row/cell schema to support optional expansion (int) and notSelectable (bool) per cell
• Options: add to TableData.Rows as richer structure, or introduce cellOptions map by (row,col)
• In populateTableData, call SetExpansion and SetSelectable(false) on TableCell when configured

Relevant Files

• config/types.go – extend TableData or add cell metadata
• builder/builder.go – populateTableData
• docs/tview-coverage.md – document once implemented