Codex-style pinned sessions for DeepSeek Harness

Key features

• Newest pin is listed first.
• Pins persist in localStorage (dsh-codex-pins.v1), per browser origin.
• If you previously used dsh-session-pin, existing local pins are imported once.
• Stale ids are dropped when the session catalog is ready.
• UI-onlyno model traffic, no host HTTP routes, no session-log reads, no install scripts.