fix(security): read AMD credentials from environment variables - #1018

Reviewer bee Y: code is sound, not merged.

• origin/main still sends a hardcoded AMD account e-mail and password in fpga/fly-vivado/setup_and_synth.exp. This PR replaces both with $env(AMD_USER) / $env(AMD_PASS) (valid Tcl/expect inside double quotes). 1 file, +3/-2, matches the title.
• Blocker: required status T27 work report is FAILURE ('Missing, stale or invalid work report'). The author must add a valid work report to the body; a reviewer writing it would become its author.
• The password is public in history: it must be rotated at AMD regardless.

bee review (closing as superseded). Head 539c028, CONFLICTING.

The change is already on main: #1258 (7511cc7, "fix(security): strip plaintext credentials from the tree") rewrote fpga/fly-vivado/setup_and_synth.exp to read AMD_ACCOUNT_EMAIL / AMD_ACCOUNT_PASSWORD from the environment and to refuse to run without them. This PR's AMD_USER/AMD_PASS variant would now only conflict.

Security note: the removed lines of this diff carry a plaintext account e-mail and password (values not repeated here). Removing them from the tree does not remove them from git history or from this PR's diff, so the AMD account password must be treated as exposed and rotated. Not merged for that reason as well.