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/debug-client/src/client.rs

@@ -187,7 +187,7 @@ impl AppServerClient {
                 thread_id: thread_id.to_string(),
                 input: vec![UserInput::Text {
                     text,
-                    // Plain text conversion has no UI element ranges.
+                    // Debug client sends plain text with no UI markup spans.
                     text_elements: Vec::new(),
                 }],
                 ..Default::default()