fix(settings): mirror env var changes to os.environ on http save path
The HTTP /api/config save path wrote provider keys to journal.json but
never updated os.environ in the running supervisor — so a key saved via
the localhost:5015 wizard validated successfully yet /api/providers and
sol call settings providers reported configured:false until restart.
Mirrors the cli pattern in apps/settings/call.py:362-394 (set/clear).
After this, the wizard is self-sufficient — no service restart required
after pasting a key on a fresh install.
Regression test asserts os.environ reflects both set and clear in-process
through the http endpoint.
Refs req_uf5stjw7.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>