feat: add Table SetSelectable(row, col) config

[cassdeckard]

Summary

Add configuration for Table's SetSelectable(selectRows, selectColumns) so both row-only, column-only, and cell selection modes can be expressed in YAML. tviewyaml currently only supports row-selectable mode.

Background

Discovered while planning a tview presentation demo implementation via tviewyaml. The Table slide toggles between (true, false), (false, true), and (true, true) to demonstrate selection modes.

Demo Usage

Demo toggles (true,false), (false,true), (true,true); tviewyaml only supports row-selectable.

Proposed Approach

• Add selectRows: true/false and selectColumns: true/false to Table primitive config (default both false, or match current row-only behavior)
• In builder/builder.go, call SetSelectable(selectRows, selectColumns) when building table

Relevant Files

• config/types.go – add selectRows, selectColumns
• builder/builder.go – populateTableData, buildTable
• docs/tview-coverage.md – document once implemented