Add optional dynamic conversation titles via a model rename capability

Summary

Codex should optionally expose a model-usable tool/capability for dynamically renaming the current conversation as the work evolves.

Problem

Static or one-time titles are often insufficient once a session changes direction. Even with manual rename support, the title can drift out of sync with the actual work unless the user keeps updating it themselves.

Requested behavior

• add an optional capability/tool that allows the model to rename the current conversation/thread
• expose it as a user-controlled feature, for example "Dynamic Conversation Title"
• allow prompting/guidance that encourages the model to keep the title aligned with the current work as the task evolves
• keep manual rename available and let the user override the dynamic title at any time

Why this is useful

• long sessions often change scope or become more specific over time
• dynamic titles would improve resume/search/navigation across many threads
• it reduces the need for the user to manually keep titles synchronized with the actual work

Suggested UX / policy direction

• off by default or clearly opt-in
• model updates title only when the conversation meaningfully changes
• avoid noisy micro-renames on every tiny turn
• title changes should be visible/auditable in the UI

Success criteria

• a session can keep a useful current title without manual renaming every time the scope shifts
• the feature is controllable by the user
• manual rename and dynamic rename coexist cleanly
• title changes improve session navigation rather than creating churn

Related context

• #9471
• #4163

This request was suggested in the discussion on #9471 as a separate feature request.