feat: time estimation & tracking

[h4yfans]

Summary

estimatedMinutes and timeSpent fields for workload planning. Cannot plan workload or review time allocation.

Scope

• Add estimated_minutes and time_spent_minutes to tasks table
• Timer UI in task detail drawer (start/stop/pause)
• Daily/weekly time summary view
• Workload bar per project

Complexity

Medium

DB Changes

Migration for 2 new columns + field clocks

Acceptance Criteria

• Two new columns added via Drizzle migration
• Field clocks updated for new fields (Phase 8 compat)
• Timer component in task detail (start/stop/pause)
• Time display formatted (1h 30m, not 90m)
• Daily summary: total time per project
• Weekly summary view with bar chart
• Workload bar on project list/header

Priority

#6 — Differentiator for productivity-focused users