Preserve base instruction provenance across sessions (#37446)

## Why

Persisted base instructions need to retain whether they were explicitly customized or generated from a model template. Without that distinction, forks and config-lock replays can treat model-generated instructions as custom and keep the wrong template after a model or personality change.

## What changed

- Record custom or model provenance with base instructions in rollouts and config locks.
- Preserve custom instructions across model changes, while allowing model-generated instructions to follow the selected model and personality.
- Keep legacy rollouts without provenance compatible and propagate provenance through forks and spawned agents.

## Testing

- Cover provenance serialization and legacy rollout decoding.
- Cover role personality changes, forked model changes, config-lock replay, and multi-agent configuration.

GitOrigin-RevId: 801c26559835f558027ce5112700c0cd31fcb21b

codex-rs/memories/write/src/phase1.rs

@@ -307,6 +307,7 @@ mod job {
         }];
         prompt.base_instructions = BaseInstructions {
             text: crate::stage_one::PROMPT.to_string(),
+            provenance: None,
         };
         prompt.output_schema = Some(output_schema());
         prompt.output_schema_strict = true;