fix: Codex model catalog WYSIWYG and config consolidation

- Remove mergeCodexDefaultCatalogModelForSave implicit injection (P1)
  The model mapping table is now the single source of truth; no hidden
  entries are prepended on save.

- Sync first catalog row model into config.toml on save
  Ensures Codex default request model matches the table's first entry
  instead of retaining a stale template value.

- Remove API Format selector from CodexFormFields (P3)
  wire_api is always 'responses'; the selector confused users into
  thinking they were changing the upstream protocol. Only the 'Needs
  Local Routing' toggle remains.

- Add restart hint to model mapping i18n text (P2)
  model_catalog_json is loaded at Codex startup; users are now informed
  that a restart is needed after changes.

- Unify write_codex_live_with_catalog helper (P4)
  Replaces three scattered prepare+write call sites in config.rs,
  provider/live.rs, and proxy.rs with a single entry point.

- Clean up useCodexConfigState dead state (P3 follow-up)
  Remove codexModelName, codexContextWindow, codexAutoCompactLimit and
  their handlers/effects since no component consumes them after the UI
  consolidation.