feat: add customizable category tags to Goal Tracker (#2647)

[aaniya22]

Summary

Adds customizable category tags (Side Project, Work, DSA, Open Source) to the Goal Tracker widget so users can categorize goals and filter their view by a single tag, as requested in the issue.

Closes #2647

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• supabase/migrations/20260713010000_add_goal_category.sql — adds a nullable category column to goals (constrained to side-project, work, dsa, open-source) plus a supporting index; mirrored the same column/index in supabase/schema.sql for the canonical schema.
• src/app/api/goals/route.ts — validates category on POST /api/goals (falls back to null for unrecognized values), persists it on insert, and includes it in the goal.created webhook payload.
• src/lib/goal-tracker.ts — extended CreateGoalPayload with an optional category field and exported a GoalCategory type.
• src/components/GoalTracker.tsx:
  • Added a "Category (Optional)" dropdown to the goal creation form.
  • Added a color-coded micro-badge next to the goal title on each card when a category is set.
  • Added a row of toggle filter pills (All + one per category) above the goal list, shown only when at least one goal has a category, to filter the view by a single tag.

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How to Test

1. Pull this branch and run the new migration (supabase/migrations/20260713010000_add_goal_category.sql) against your local/dev Supabase instance.
2. Open the dashboard, expand the Goal Tracker widget, and create a new goal — select a category (e.g. "DSA") from the new dropdown.
3. Confirm the goal renders with a color-coded "DSA" badge next to its title, and that a filter pill row appears above the list.
4. Click the "DSA" pill and confirm only goals tagged DSA are shown; click it again (or click "All") to clear the filter.
5. Create a goal with no category selected and confirm it renders without a badge and is hidden when a specific category filter is active.

Expected result: Goals can optionally be tagged with one of four categories at creation time, tags render as badges on the goal card, and the filter pills let a user isolate goals by a single tag.

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Screenshots / Recordings

Before	After
(flat, uncategorized goal list)	(add screenshot showing category dropdown + badges + filter pills)

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

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Accessibility (UI changes only)

• Keyboard navigation works correctly (filter pills and select are native focusable elements)
• Color contrast meets WCAG AA standard
• ARIA labels / roles added where needed (role="group", aria-label, aria-pressed on filter pills)
• Tested on mobile / responsive layout

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Additional Context

Category is optional and additive — existing goals without a category continue to work unchanged, and the filter row only appears once at least one goal has a tag, so the UI stays uncluttered for users who don't use this feature. I haven't run npm run lint / type-check or added tests locally yet — please run those on your machine before merging, and let me know if you'd like me to add a unit test for the category validation logic in the API route.

[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