fix(envdsmoke): pick the envd user with the SDK's Basic auth header

[CMGS]

envd takes the process user from Authorization: Basic base64(user:), which is the header the e2b SDK sends. It ignores X-User, so every process the smoke started ran as root, and the user-account step failed on hardware:

envdsmoke: user account with sudo: the user account reports "root\n/root\nsudo\n", want user, /home/user and passwordless sudo

The two X-User headers become Authorization: Basic ….

Hardware (scripts/envd-e2e.sh, sandboxd at sandbox main 7dd89ae6, isolated cocoon root):

• master 774a233: e2b-rt and e2b-ci both FAIL at the user-account step.
• this branch: e2b-rt ENVDSMOKE PASS; e2b-ci (medium, CODE_INTERPRETER=1) ENVDSMOKE PASS, including interpreter runs 1+1.

Gates: make lint 10× 0 issues., make fmt-check clean, asl 0 on darwin and linux.