Add interactive project selection when running commands outside a known project directory.

Parent task: #336
Depends on: #339 (Project registry), Subtask 3.5

Details

When running rover task or similar commands outside a git repo or known project:

• Interactive mode: Show list of registered projects for user to select
• Non-interactive mode: Fail with message to use --project flag

Also prompt for project selection when:

• Multiple projects could apply
• User wants to create a task in a different project

TODO

• Detect interactive vs non-interactive environment
• Implement project selection prompt using enquirer
• Show project list with names, paths, and recent activity
• Add "Register new project" option in prompt
• Fail gracefully in non-interactive mode with guidance
• Add tests for interactive selection flow