Persist text elements through TUI input and history (#9393)

Continuation of breaking up this PR
https://github.com/openai/codex/pull/9116

## Summary
- Thread user text element ranges through TUI/TUI2 input, submission,
queueing, and history so placeholders survive resume/edit flows.
- Preserve local image attachments alongside text elements and rehydrate
placeholders when restoring drafts.
- Keep model-facing content shapes clean by attaching UI metadata only
to user input/events (no API content changes).

## Key Changes
- TUI/TUI2 composer now captures text element ranges, trims them with
text edits, and restores them when submission is suppressed.
- User history cells render styled spans for text elements and keep
local image paths for future rehydration.
- Initial chat widget bootstraps accept empty `initial_text_elements` to
keep initialization uniform.
- Protocol/core helpers updated to tolerate the new InputText field
shape without changing payloads sent to the API.

codex-rs/tui2/src/transcript_view_cache.rs

@@ -1018,6 +1018,8 @@ mod tests {
         let mut cache = TranscriptViewCache::new();
         let cells: Vec<Arc<dyn HistoryCell>> = vec![Arc::new(UserHistoryCell {
             message: "hello".to_string(),
+            text_elements: Vec::new(),
+            local_image_paths: Vec::new(),
         })];
 
         cache.ensure_wrapped(&cells, 20);