Add milestone achievements to dashboard

[singhanish08]

Description

Fixes #162

Added milestone-based achievements for contribution totals and streak lengths in the dashboard.

Changes Made

• Added milestone generation logic for:

  • Contributions (100, 250, 500, 1000)
  • Streaks (7, 30, 100)

• Added achievement progress tracking

• Integrated achievements into dashboard response data

• Replaced placeholder achievements with dynamic milestone achievements

• Updated Achievements UI to display milestone progress

• Added tests for milestone generation logic

Pillar

• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

Added dynamic milestone achievement cards with:

• contribution milestones
• streak milestones
• locked/unlocked states
• progress indicators

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (localhost:3000/api/streak?user=YOUR_USERNAME).
• I have run npm run format and npm run lint locally and resolved all errors (CI will fail otherwise).
• My commits follow the Conventional Commits format (e.g., feat(themes): ..., fix(calculate): ...).
• I have updated README.md if I added a new theme or URL parameter.
• I have started the repo.
• I have made sure that i have only one commit to merge in this PR.
• The SVG output matches the CommitPulse "premium quality" aesthetic standard (no raw elements, smooth animations, correct fonts).
• (Recommended) I joined the CommitPulse Discord community for contributor discussions, mentorship, and faster PR support.

[github-actions]

👋 Hey @singhanish08, welcome to CommitPulse! 🎉

Thanks for opening your first pull request — this is a big deal and we appreciate the effort!

While you wait for a review, please double-check:

• ✅ You've read the CONTRIBUTING.md checklist
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