docs: add CHANGELOG.md and update contribution guidelines

[SamakhyaPathak]

Summary [required]

Added a new CHANGELOG.md file to the repository root following the Keep a Changelog format for documenting notable project updates and future changes.

Also updated CONTRIBUTING.md to remind contributors to update the changelog whenever they make user-facing or documentation-related changes.

This improves documentation consistency and helps maintain a structured history of project updates for future contributors and maintainers.

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Related Issue [required]

Closes #88

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Type of Change [required]

• Bug fix — resolves a broken behaviour
• Feature — adds new functionality
• Data — adds new projects to data/projects.json
• Documentation — updates docs, README, or code comments only
• Style — CSS or visual changes only, no logic change
• Refactor — restructures code without changing behaviour
• Test — adds or updates tests

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What Was Changed [required]

File	Change made
CHANGELOG.md	Added a new changelog file following the Keep a Changelog structure
CONTRIBUTING.md	Added a contributor reminder to update CHANGELOG.md for relevant changes

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How to Test This PR [required]

1. Clone this branch:
   git checkout docs/add-changelog

2. Install dependencies:
   pip install -r requirements.txt

3. Verify that CHANGELOG.md exists in the repository root.

4. Open CHANGELOG.md and confirm:

   • markdown formatting is correct
   • sections follow the Keep a Changelog structure
   • headings render properly

5. Open CONTRIBUTING.md and verify the changelog reminder exists under:
   Before opening a PR

6. Run the test suite:
   python tests/test_basic.py

Expected test output:

27 passed, 0 failed out of 27 tests

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Test Results [required]

PASS test_projects_json_loads
PASS test_each_project_has_required_fields
PASS test_find_project_by_id_found
PASS test_find_project_by_id_missing
PASS test_parse_skills_basic
PASS test_parse_skills_empty_string
PASS test_parse_skills_single_entry
PASS test_score_single_project_full_match
PASS test_score_single_project_no_match
PASS test_get_recommendations_returns_results
PASS test_get_recommendations_max_three
PASS test_get_recommendations_no_match_returns_empty
PASS test_get_recommendations_result_format
PASS test_validate_all_valid
PASS test_validate_missing_skills
PASS test_validate_missing_level
PASS test_validate_missing_interest
PASS test_validate_missing_time
PASS test_validate_all_missing
PASS test_home_route
PASS test_recommend_api_valid
PASS test_recommend_api_missing_field
PASS test_recommend_api_empty_body
PASS test_project_detail_found
PASS test_project_detail_not_found
PASS test_view_code_found
PASS test_download_code_found

27 passed, 0 failed out of 27 tests

Self-Review Checklist [required]

• I have read CONTRIBUTING.md and followed all guidelines
• My branch name follows the convention: feat/, fix/, docs/, data/, style/, test/
• I have run python tests/test_basic.py and all 27 tests pass
• I have run flake8 . locally and there are no errors
• I have not introduced any print() or console.log() debug statements
• Every new function I wrote has a docstring
• I have not modified files outside the scope of the linked issue
• If I changed the UI, I tested it at 375px (mobile) and 1280px (desktop)
• If I added a project to the dataset, it has all required JSON fields

Notes for Reviewer

This PR only introduces documentation-related changes and does not modify application logic, tests, templates, routes, or UI behaviour.

The changelog entries were intentionally kept minimal and accurate to avoid adding undocumented or non-existent historical project changes.

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@SamakhyaPathak is attempting to deploy a commit to the komalsony234-1530's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Thank you for submitting your first pull request to DevPath.

Before review:

• Complete the PR template fully
• Ensure all tests pass
• Link your PR to an issue
• Keep changes scoped to the issue

A maintainer will review your contribution soon.

[komalharshita]

Thank you for the contribution. This is a clean and well-scoped documentation improvement.

Adding a structured CHANGELOG.md improves long-term project maintainability and contributor coordination, and the update to CONTRIBUTING.md aligns properly with the new documentation workflow.

I also appreciate that the PR follows an established changelog convention instead of introducing a custom structure.

The implementation is lightweight, consistent, and safe to merge.