[codex-analytics] guardian review analytics schema polishing (#17692)

## Why

Guardian review analytics needs a Rust event shape that matches the
backend schema while avoiding unnecessary PII exposure from reviewed
tool calls. This PR narrows the analytics payload to the fields we
intend to emit and keeps shared Guardian assessment enums in protocol
instead of duplicating equivalent analytics-only enums.

## What changed

- Uses protocol Guardian enums directly for `risk_level`,
`user_authorization`, `outcome`, and command source values.
- Removes high-risk reviewed-action fields from the analytics payload,
including raw commands, display strings, working directories, file
paths, network targets/hosts, justification text, retry reason, and
rationale text.
- Makes `target_item_id` and `tool_call_count` nullable so the Codex
event can represent cases where the app-server protocol or producer does
not have those values.
- Keeps lower-risk structured reviewed-action metadata such as sandbox
permissions, permission profile, `tty`, `execve` source/program, network
protocol/port, and MCP connector/tool labels.
- Adds an analytics reducer/client test covering `codex_guardian_review`
serialization with an optional `target_item_id` and absent removed
fields.

## Verification

- `cargo test -p codex-analytics
guardian_review_event_ingests_custom_fact_with_optional_target_item`
- `cargo fmt --check`

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/17692).
* #17696
* #17695
* #17693
* __->__ #17692

codex-rs/core/src/guardian/mod.rs

@@ -19,6 +19,7 @@ mod review_session;
 use std::time::Duration;
 
 use codex_protocol::protocol::GuardianAssessmentDecisionSource;
+use codex_protocol::protocol::GuardianAssessmentOutcome;
 use serde::Deserialize;
 use serde::Serialize;
 
@@ -45,14 +46,6 @@ const GUARDIAN_MAX_ACTION_STRING_TOKENS: usize = 16_000;
 const GUARDIAN_RECENT_ENTRY_LIMIT: usize = 40;
 const TRUNCATION_TAG: &str = "truncated";
 
-/// Final allow/deny outcome returned by the guardian reviewer.
-#[derive(Debug, Clone, Copy, Deserialize, Serialize, PartialEq, Eq)]
-#[serde(rename_all = "lowercase")]
-pub(crate) enum GuardianAssessmentOutcome {
-    Allow,
-    Deny,
-}
-
 /// Structured output contract that the guardian reviewer must satisfy.
 #[derive(Debug, Clone, Deserialize, Serialize)]
 pub(crate) struct GuardianAssessment {