Fix navigating to Collab URLs not working when not connected

[probably-neb]

Objective

• Fix collab channel links opened from URL actions or the CLI when Zed is signed in but not currently connected to the collab server.

Solution

• Connect to collab before handling channel joins or channel notes links.
• Keep downstream errors visible if connecting or opening still fails.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

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Release Notes:

• Fixed opening collab links when Zed is not already connected to the collaboration server.