feat(app): add pinned workspaces in sidebar

[anduimagui]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

the desktop app makes it really easy to tinker with a specific feature or fix on a separate workspace / worktree - this adds basic workspace pinning in the sidebar to keep better track of what work is a priority.

• You can now toggle Pin / Unpin from the workspace menu.
• Pinned workspaces are shown first.
• There is now a simple visual separator between pinned and unpinned groups.
• Pin state is persisted per project root.
• Drag/reorder stays within the same group (pinned with pinned, unpinned with unpinned).

How did you verify your code works?

• Ran bun typecheck in packages/app
• Ran bun test:e2e -- projects/workspaces.spec.ts -g "can pin and unpin a workspace with persistence" --list
• Push pre-hook bun turbo typecheck passed

Screenshots / recordings

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[anduimagui]

I'm out of my depth on UI prioritization / details, so I intentionally kept the grouping UI minimal for now (just a basic separator) to keep this safe and easy to iterate on. keen to hear your thoughts @iamdavidhill @adamdotdevin