Problem / Background

TUI sub-item rows use inconsistent indentation across the different renderers:

• gpu_renderer.rs (thermal/P-state row, hardware details row): 5-space indent
• vgpu_renderer.rs (vGPU instance rows): 6-space indent
• mig_renderer.rs (MIG instance rows): 6-space indent
• Section headers in vGPU/MIG renderers: 2-space indent

This produces a visually inconsistent hierarchy when viewing GPUs with both thermal data and vGPU/MIG sub-instances.

Goal

Standardize all sub-item indentation to a single consistent value across GPU, vGPU, and MIG renderers.

Scope

• Define a shared constant (e.g., const SUB_ITEM_INDENT: &str = " ") for sub-item rows
• Define a shared constant for section headers
• Apply consistently across gpu_renderer.rs, vgpu_renderer.rs, mig_renderer.rs
• Verify visual consistency in the TUI with mock data