remove temporary ownership re-exports (#16626)

Stacked on #16508.

This removes the temporary `codex-core` / `codex-login` re-export shims
from the ownership split and rewrites callsites to import directly from
`codex-model-provider-info`, `codex-models-manager`, `codex-api`,
`codex-protocol`, `codex-feedback`, and `codex-response-debug-context`.

No behavior change intended; this is the mechanical import cleanup layer
split out from the ownership move.

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/utils/sandbox-summary/Cargo.toml

@@ -9,6 +9,7 @@ workspace = true
 
 [dependencies]
 codex-core = { workspace = true }
+codex-model-provider-info = { workspace = true }
 codex-protocol = { workspace = true }
 
 [dev-dependencies]