feat: Separate XGMI and NVLINK to an independent tab

[crazyguitar]

Purpose

Add RDMA/XGMI/NVLink tabs (Tab/Shift-Tab to switch; a tab only appears when its hardware is detected) and drop the nvlink/xgmi cargo features — both backends load at runtime, so one binary serves every host.

Test Plan

8× MI325X: default-build test suite + hardware smoke test; TUI capture shows the RDMA │ XGMI bar with no amdgpu rows on the RDMA tab; Tab switching eyeballed (cycling/detection covered by unit tests).

Test Result

Checklist

• cargo fmt --check passes
• cargo clippy -- -D warnings passes
• cargo test passes
• Tested on RDMA-capable hardware (or explained why not in the Test Plan)
• Docs/README updated if behavior or flags changed

[Copilot]

Pull request overview

This PR refactors the TUI to present RDMA, XGMI, and NVLink as separate runtime-detected tabs (Tab / Shift-Tab), and removes the nvlink/xgmi Cargo features so a single binary can run across hosts regardless of detected hardware.

Changes:

• Introduces DeviceClass and filters displayed rows by the active tab, with “seen tabs” detected/sticky per session.
• Adds a tab bar UI and a fixed-column GPU table for XGMI/NVLink, while keeping RDMA’s configurable columns.
• Removes feature-gating for NVLink/XGMI modules and dependencies; updates comments/docs accordingly.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/tui/app.rs	Adds DeviceClass, tab state, filtering, and tab-cycling logic.
src/tui/events.rs	Adds Tab / BackTab key handling in normal mode.
src/tui/ui.rs	Adds tab bar rendering, GPU table rendering, header label tweaks, and help sizing changes.
src/tui/theme.rs	Removes the unused group_title theme color.
src/main.rs	Always compiles nvlink module (no feature gating).
src/nvlink.rs	Updates module docs to reflect runtime loading behavior.
src/xgmi.rs	Updates module/docs/tests text to remove feature-flag references.
Cargo.toml	Drops nvlink/xgmi features and makes deps non-optional.
examples/pytorch/README.md	Updates installation instructions to remove feature flags.

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