feat: Order projects by most recently used (Vibe Kanban)

[britannio]

Summary

This PR updates the project listing to order projects from most to least recently used, improving discoverability of active projects.

Changes

• Modified Project::find_all() in crates/db/src/models/project.rs to order projects by recent task activity
• Uses a LEFT JOIN with a subquery that finds the maximum task_attempts.updated_at per project
• Projects with recent task activity appear first
• Projects without any task activity fall back to ordering by created_at DESC

Implementation Details

The query uses:

LEFT JOIN (
    SELECT t.project_id, MAX(ta.updated_at) as last_activity
    FROM tasks t
    INNER JOIN task_attempts ta ON ta.task_id = t.id
    GROUP BY t.project_id
) activity ON activity.project_id = p.id
ORDER BY activity.last_activity DESC NULLS LAST, p.created_at DESC

This approach:

• Avoids direct GROUP BY on the main query which causes SQLx type inference issues
• Uses NULLS LAST to ensure projects without activity appear after active ones
• Preserves chronological ordering (newest first) for projects with no task attempts

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This PR was written using Vibe Kanban

[isomoes]

when merge? need it.