On Windows process.env/Bun.env lookups are case-insensitive, so the
"env var name, else literal" resolvers turned a literal /login key like
`public` (OpenCode Zen's free key) into the built-in PUBLIC=C:\Users\Public,
sending `Authorization: Bearer C:\Users\Public` and 401ing every request.
Added `$envExact` in pi-utils, which trusts an env lookup only when an
exact-case key is enumerated (the only case-preserving signal on Windows;
the getter and hasOwnProperty/getOwnPropertyDescriptor traps are all
case-insensitive there). Wired it into all three resolvers:
resolve-config-value.ts, model-registry.ts, and auth-storage.ts.
Fixes#7361
roboomp
a6521f07ed