memories: focus write prompts on user preferences (#14493)

## Summary
- update `codex-rs/core/templates/memories/stage_one_system.md` so phase
1 captures stronger user-preference signals, richer task summaries, and
cwd provenance without branch-specific fields
- update `codex-rs/core/templates/memories/consolidation.md` so phase 2
keeps separate sections for user preferences, reusable knowledge, and
failure shields while staying cwd-aware but branchless
- document the `codex` prompt-template maintenance rule in
`codex-rs/core/src/memories/README.md`: the undated templates are
canonical here and should be edited in place

## Testing
- cargo test -p codex-core memories --manifest-path codex-rs/Cargo.toml

codex-rs/core/src/memories/README.md

@@ -2,6 +2,18 @@
 
 This module runs a startup memory pipeline for eligible sessions.
 
+## Prompt Templates
+
+Memory prompt templates live under `codex-rs/core/templates/memories/`.
+
+- The undated template files are the canonical latest versions used at runtime:
+  - `stage_one_system.md`
+  - `stage_one_input.md`
+  - `consolidation.md`
+  - `read_path.md`
+- In `codex`, edit those undated template files in place.
+- The dated snapshot-copy workflow is used in the separate `openai/project/agent_memory/write` harness repo, not here.
+
 ## When it runs
 
 The pipeline is triggered when a root session starts, and only if: