Handle credential provider source remapping across config layers (#44241)

## What changed

- Let higher-priority providers in `features.network_proxy.credentials` displace lower-priority providers with overlapping `env` sources, including in profiles. Preserve inherited settings when providers swap sources, and compare environment names case-insensitively on Windows.
- Preserve provider definitions across ordered batch remaps and persist displaced-provider removals without overwriting unrelated sibling updates.
- Validate remapped providers using the credential broker's compilation rules before persisting writes, while allowing incomplete drafts and explicit deletions.
- Omit displaced providers from config origins and report writes overridden by another provider's source ownership.
- Build trusted credential-broker configuration before merging managed layers for project discovery, preserving remapped providers' environment protections.

## Testing

Add unit and config RPC regression tests for source precedence, source swaps, ordered edits, concurrent sibling updates, atomic rejection of invalid remaps, persistence, and override reporting. Add a macOS managed-config regression test for remapped provider bindings during project discovery.

GitOrigin-RevId: b7d402727acf4e5b0f25946db1cf18811f5e2679

codex-rs/app-server/Cargo.toml

@@ -40,6 +40,7 @@ codex-aws-auth = { workspace = true }
 codex-cloud-config = { workspace = true }
 codex-code-mode = { workspace = true }
 codex-config = { workspace = true }
+codex-network-proxy = { workspace = true }
 codex-connectors = { workspace = true }
 codex-core = { workspace = true }
 codex-core-plugins = { workspace = true }