fix(session): fix unshare command not clearing share state

[Raviguntakala]

Summary

Fix sharing-related issues: unshare command not working and wrong share URL displayed

Changes

Commit 1: fix unshare command (Fixes #5493)

• Fixed code path mismatch: unshare now uses ShareNext.remove() like share does
• Fixed storage key bug in ShareNext.remove() (was using wrong key)
• Added toast feedback for unshare command

Commit 2: fix share URL display (Fixes #5522)

• --share flag was showing hardcoded URL opencode.ai/s/xxx
• Now shows actual URL from API response opncd.ai/share/xxx