#3080 setup: recognize the Instinct MI50 / MI60 / Radeon VII (gfx906) as a supported card

Description

Setup-side enablement only — no speed claim, no builder branch: `setup.py` lists gfx906 as a supported card and points at the hand build. The TheRock wheels do not ship gfx906 and the wheel path is 7.x-only, so a system ROCm 6.x + `cmake` build is the only path for this card (documented in `docs/AMD_HIP.md`, added by #3077). `tools/test_setup_amd.py` encodes the no-wheels exception.

**What it changes**

- `AMD_ARCHS` / `AMD_NAMES` / `AMD_CARDS` gain gfx906; the card text notes a system ROCm 6.x is required (the wheel path does not carry this arch).
- `tools/test_setup_amd.py` gains the gfx906 no-wheels exception cases.

**What it leaves alone**: every other card's path is unchanged; the wheel-driven default path is untouched. The card is opt-in by nature — setup lists it and points at the hand build, it does not drive one.

Verified: `python tools/test_setup_amd.py` passes (40 tests), including the new exception cases. Engine-side build/run evidence for the card is in `docs/ROCm_6_3_3.md` (#3077) on 2x MI50.

Merge order note: references `docs/ROCm_6_3_3.md` from #3077 in the card text, so that one should land first.

Related: #2883 (community gfx906 validation).