feat(codex): align ccsxp with native cliproxy shortcut

docs/system-architecture/index.md

@@ -101,7 +101,7 @@ ccs-droid  → Target: droid (explicit alias)
 ccsd       → Target: droid (legacy shortcut)
 ccs-codex  → Target: codex (explicit alias)
 ccsx       → Target: codex (short alias)
-ccsxp      → Target: codex (provider shortcut; rewrites argv to `ccs codex --target codex`)
+ccsxp      → Target: codex (native cliproxy shortcut; prepends `--config model_provider="cliproxy"`)
 ```
 
 For details on the adapter architecture, see [Target Adapters](./target-adapters.md).

docs/system-architecture/target-adapters.md

@@ -88,7 +88,7 @@ CCS resolves which adapter to use via priority-ordered checks:
 2. Explicit runtime entrypoint (`CCS_INTERNAL_ENTRY_TARGET`) — dedicated bin shims
    └─ ccs-droid / ccsd → droid
    └─ ccs-codex / ccsx → codex
-   └─ ccsxp → codex, then rewrites argv to `ccs codex --target codex ...`
+   └─ ccsxp → codex, then prepends `--config model_provider="cliproxy"`
 
 3. argv[0] detection (runtime alias pattern) — binary name mapping for same-binary/custom aliases
    └─ ccs-droid (explicit alias) → droid
@@ -514,7 +514,7 @@ ccsx
 ccsxp
 → dist/bin/ccsxp-runtime.js
 → CCS_INTERNAL_ENTRY_TARGET=codex
-→ injects built-in codex profile shortcut
+→ injects native `model_provider="cliproxy"` override
 → pins CODEX_HOME to native `~/.codex` unless `CCSXP_CODEX_HOME` is set
 ```