feat(app): add project pinning to sidebar menu

[anduimagui]

Issue for this PR

Closes #11759

Type of change

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

What does this PR do?

Adds a right-click pin/unpin action to the project sidebar menu and persists that state in the app server store. Pinned projects stay grouped at the top, and drag reordering now stays within the pinned and unpinned sections so this remains scoped to project pinning without bringing in the broader dynamic sorting work.

How did you verify your code works?

• Ran bun run typecheck in packages/app
• Ran bun run build in packages/app

Screenshots / recordings

Not included.

Checklist

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

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate PRs Found

1. PR #16068: feat(app): add pinned workspaces in sidebar

• feat(app): add pinned workspaces in sidebar #16068
• Why related: Very similar feature - adds pinning capability to sidebar items. This appears to be addressing a related or overlapping functionality for pinning workspaces/projects.

2. PR #11758: feat(app): add dynamic sidebar sorting for active projects and sessions

• feat(app): add dynamic sidebar sorting for active projects and sessions #11758
• Why related: Related to sidebar sorting and organization of projects. The current PR mentions keeping drag reordering scoped to pinning rather than bringing in broader dynamic sorting work, suggesting this PR (11758) may be addressing similar organizational concerns.