feat(projects): finish multi-repository workspace flows

[thomaspblock]

Summary

• seed new project homes with a built-in operational canvas while preserving custom templates and None
• make category create actions open the matching project-aware modal and keep selection presentation type-specific
• aggregate Tasks and Commits across every repository with responsive project/repository grouping and a repository Overview tab

This is the final part of the channel-first Projects stack, based on #6600.

Testing

• focused project template, work-item aggregation, and overview-context tests: 16/16 passed
• Desktop unit suite: 5,455/5,455 passed
• E2E-mode Desktop build passed
• TypeScript, Biome, and differential file-size checks passed
• full pre-push gate passed

Post-Deploy Monitoring & Validation

• create a project, inspect its canvas, and exercise Tasks/Commits across a project with several repositories
• healthy signals: populated project canvas, one chronological commit list with repository attribution, and complete task aggregation
• failure signals: missing canvas, single-repository-only counts, duplicate repository groups, or category actions opening the wrong flow; mitigate by reverting this PR