feat: goal completion history & analytics - trend chart with avg completion rate #2121

[IshitaSingh0822]

Summary

Added goal history tracking and analytics to DevTrack. Users can now view weekly completion trends per goal via a collapsible line chart powered by Recharts. Includes a new Supabase table, API route, and GoalHistory component.
Closes #2121

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Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

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Changes Made

• Added GoalHistory.tsx — collapsible section with a Recharts <LineChart> showing weekly completion % per goal (color-coded lines, one per goal)
• Added GET /api/goals/history?weeks=8 route — returns last N weeks of completion data per goal with goal metadata for labeling
• Added supabase/migrations/20250607_goal_history.sql — creates goal_history table with user/goal foreign keys and index on (user_id, period_end desc)
• Updated GoalTracker.tsx to render <GoalHistory /> at the bottom of the goals card
• Average completion % over last 4 weeks computed and displayed above the chart
• Designed as one unified chart for all goals (cleaner UX than per-goal expandable sections)

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How to Test

1. Create a recurring (weekly/monthly) goal in DevTrack
2. Let a period complete so a goal_history row is inserted
3. Open the Goals card and click "Goal History & Analytics" at the bottom
4. Verify the line chart renders with correct week labels and completion %
5. Verify "Average completion last 4 weeks" stat appears above the chart
6. Verify empty state shows when no history exists
7. Verify the section is collapsed by default

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Screenshots (if UI change)

N/A — chart renders only when goal_history rows exist; empty state shown otherwise.

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Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

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Accessibility Checklist

• Proper keyboard navigation tested
• Responsive UI verified
• Accessibility labels added where needed (aria-expanded on toggle button, aria-hidden on decorative SVGs)

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Additional Notes

• Chart handles < 2 weeks of data gracefully via connectNulls on Recharts <Line> — no crash on sparse data
• One unified history chart preferred over per-goal expandable buttons for cleaner dashboard UX
• Table named goal_history (not goal_completions as in the issue spec) — consistent with the API route query

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Priyanshu-byte-coder]

This PR now has a merge conflict with main after recent changes to GoalTracker.tsx were merged.

Please rebase your branch on main to resolve the conflicts:

git fetch origin
git rebase origin/main

Once CI passes, we can merge this.