Copilot no longer overwrites manual conflict resolution

Added

• Add Copilot usage info, moving custom provider configuration into a link from the Copilot model picker and adding better support for accounts with multiple Copilot licenses

Fixed

• Disable Continue in the Copilot conflict resolution dialog until every file skipped by Copilot (e.g. minified or oversized conflicts) has been resolved, and list those files separately for manual resolution
• Stop Copilot from overwriting a conflicted file's manual resolution when the user already removed the conflict markers themselves before clicking Continue
• Copilot conflict resolution now surfaces the underlying error (sign-in, network, rate limit, timeout) instead of a generic "returned no results" message
• Show correct expanded context and syntax highlighting for resolved lines in the Copilot conflicts Changes tab instead of unrelated content
• Screen readers now announce the group label ('Main Worktree' / 'Linked Worktrees') for items in the worktree list
• Show an error message instead of an endless loading spinner when a file's diff fails to load in the Copilot conflicts Changes tab

Improved

• Copilot conflict resolution now handles delete-vs-modify conflicts, suggesting "keep" or "delete" for files deleted on one branch and modified on the other