fix: sort new threads within project lists

[k9ight000]

Problem

A newly created thread can temporarily use a client-new-thread id without a backend sort timestamp. CodexPlusPlus only corrected ordering in the top-level Chats list, so project thread lists could leave the new thread below older conversations until the temporary id settled or the app refreshed.

Fix

• Give temporary client-new-thread rows a stable provisional timestamp.
• Group visible sidebar rows by their actual Chats/project list and sort each list independently.
• Continue preferring backend updated_at_ms values when available.
• Batch /thread-sort-keys requests in groups of 200 for large sidebars.
• Add injection-script regression coverage.

Validation

• node --check assets/inject/renderer-inject.js
• cargo test -p codex-plus-core --test cdp_bridge -j 1 — 95 passed
• git diff --check

The published diff contains only the renderer injection script and its Rust regression test, and was scanned for credentials and local user paths.