fix(cli): preserve profile path_prefix when BOXLITE_API_KEY is set

[G4614]

when setting BOXLITE_API_KEY, URL/path_prefix should not be changed

Test plan

Two-sided (reverted vs applied) via three unit tests on the pure resolve_rest_options helper, the reverted side toggling it back to the bare-options logic:

• api_key_env_preserves_profile_path_prefix — profile carries path_prefix=acme + an ambient BOXLITE_API_KEY: resolved options must keep path_prefix = Some("acme") (the regression).
• api_key_env_overrides_profile_bearer_but_keeps_prefix — confirmed precedence: the bearer resolves to the env key while the prefix still survives.
• api_key_env_without_profile_has_no_prefix — no profile → no routing slot even with a key (single-tenant shape unaffected).

resolve_rest_options(profile{prefix:"acme"}, env_key)	pre-fix (bare opts in env-key branch)	post-fix (start from profile)
opts.path_prefix	None → URL /v1/boxes → 404	Some("acme") → /v1/acme/boxes
bearer credential	env key	env key (unchanged)

Precedence is unchanged where it already worked: BOXLITE_API_KEY still wins for the bearer and --url / --path-prefix flags still override the profile — the env key simply no longer discards the profile's url and routing slot.

[G4614]

Root cause — exactly which code dropped path_prefix

The bug lived entirely in the old GlobalFlags::create_runtime (src/cli/src/cli.rs:247-260 on main):

let mut opts = BoxliteRestOptions::new(url);   // bare: path_prefix = None, credential = None

// BOXLITE_API_KEY env beats stored credentials of any kind.
if let Ok(key) = std::env::var("BOXLITE_API_KEY") && !key.is_empty() {
    opts = opts.with_api_key(key);                          // ← taken whenever the env key is set
} else if let Some(profile) = stored {
    opts = crate::credentials::into_rest_options(profile);  // ← the ONLY code that copies path_prefix
    opts.url = self.url.clone().unwrap_or(opts.url);
}

into_rest_options(profile) is the only place the profile's path_prefix is carried into opts (it calls .with_path_prefix(...)). But it sits on the else if branch. The instant BOXLITE_API_KEY is present, the if branch runs instead, so opts stays the bare BoxliteRestOptions::new(url) and its path_prefix is never set — it remains None.

The later --path-prefix override (the if let Some(path_prefix) = self.path_prefix … block just below) only fires when the --path-prefix flag / BOXLITE_REST_PATH_PREFIX env is set; it does not recover the profile's value. So with an ambient BOXLITE_API_KEY and a --profile whose credential carries a path_prefix, the URL builder emits the empty-prefix /v1/boxes shape and a multi-tenant server answers 404.

In one line: the credential axis (BOXLITE_API_KEY) and the routing axis (path_prefix) were entangled in a single if/else — selecting the env-key branch silently discarded the profile's url + path_prefix instead of overriding only the bearer.

The fix in this PR decouples them: always start opts from into_rest_options(profile) (so url + path_prefix survive), then let BOXLITE_API_KEY overwrite only opts.credential.