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/core/src/event_mapping.rs

@@ -52,7 +52,7 @@ fn parse_user_message(message: &[ContentItem]) -> Option<UserMessageItem> {
                 }
                 content.push(UserInput::Text {
                     text: text.clone(),
-                    // Plain text conversion has no UI element ranges.
+                    // Model input content does not carry UI element ranges.
                     text_elements: Vec::new(),
                 });
             }