feat(tui): handle paste in session picker

[fcoury-oai]

Why

The session picker already supports typed search, but it ignored bracketed paste events entirely. On macOS terminals this makes pasted text look like a no-op on the resume screen, which is especially noticeable when a user wants to paste part of a thread name, branch, or path into the search field.

What Changed

• route TuiEvent::Paste(String) into the session picker instead of dropping it
• normalize pasted search text into a single-line query by collapsing whitespace
• ignore whitespace-only pastes
• reuse the existing set_query(...) path so pasted searches keep the same filtering and pagination behavior as typed input
• add focused tests for append behavior, whitespace normalization, whitespace-only paste, and the existing search-loading path

This PR is stacked on top of #23234 and contains only the net change relative to etraut/clarify-resume-hints.

How to Test

1. Start Codex in a terminal that emits bracketed paste, for example iTerm2 on macOS.
2. Open the resume picker so the search UI is visible.
3. Copy a term that should match one of the visible sessions, then paste it into the picker.
4. Confirm the query updates immediately and the list filters as if the text had been typed.
5. Also verify that pasting text with newlines or tabs still produces a usable single-line search query.
6. Also verify that normal typed search still works and that Esc still clears the query / exits as before.

Targeted tests:

• cargo test -p codex-tui

[canvrno-oai]

Testing by pasting test into the /resume search, worked as expected.