[project] datasets layout, detail page, timesheet seed

[xuyushun441-sys]

Remaining increments for project:

• Migrate src/data/*.data.ts to the standard datasets/-aware seed layout used by siblings (cosmetic consistency).
• Add a pm_project detail page (siblings ship one).
• Seed a few pm_timesheet rows (requires making person optional, like pm_resource) so the timesheet view + actual_cost story has demo data.

Follow-up from the 9-template optimization + 9.5.1 runtime-testing pass.