Polish Mast project home UI

[udaychandra]

Summary

• replace the expanded project details in the sidebar with a central Mast project home item
• add project home modes for Summary, Specs, Archived, Kanban, Agents, Activity, and Settings
• move refresh status into refresh control tooltips and show loading state on the control itself
• update onboarding theme selection to present the Mast theme family instead of upstream theme cards

Verification

• cargo fmt --check
• cargo check -p sing_project
• cargo check -p onboarding
• cargo test -p sing_project
• git diff --check

Notes

• Manual macOS visual inspection against the IntelliJ reference screenshot is still needed.