✨ Historical charts — issue trends and task completion over time

[fusion94]

Description

Add lightweight time-series tracking for issue counts and task completion, stored locally in SQLite.

Metrics to track

• Open issue count per day (by priority)
• Tasks completed per week
• PR cycle time
• Infra restart frequency

Acceptance Criteria

• SQLite store records snapshots on each poll cycle
• Charts rendered with a lightweight library (Chart.js or similar)
• Available as a new tab or section on Home
• No external dependencies required