feat: enhance Dockerfile security and add .dockerignore (#843)

[Aryanbansal-05]

• Add PYTHONDONTWRITEBYTECODE and PYTHONUNBUFFERED env vars
• Create non-root appuser for least-privilege execution
• Add .dockerignore to exclude venv, cache, git, IDE files

Summary [required]

This PR enhances the existing Dockerfile with security and optimization best practices, and adds a .dockerignore file to reduce the Docker build context. The container now runs as a non-root user, Python runtime is configured for cleaner container behavior, and unnecessary files like venv, pycache, and .git are excluded from builds. No application logic is affected.

Related Issue [required]

Closes #843

Type of Change [required]

• Feature — adds new functionality

What Was Changed [required]

| File | Change made |
Dockerfile | Added PYTHONDONTWRITEBYTECODE and PYTHONUNBUFFERED env vars; added non-root appuser for least-privilege execution
.dockerignore | Created new file to exclude git metadata, Python cache, venv, IDE files, and OS artifacts from build context

How to Test This PR [required]

1. Clone this branch: git checkout your-branch-name
2. Install dependencies: pip install -r requirements.txt
3. Run the app: python app.py
4. Open http://127.0.0.1:5000 and...
5. Run the tests: python tests/test_basic.py

Expected test output:

27 passed, 0 failed out of 27 tests

Test Results [required]

56 passed in 0.37s
Note: 16 pre-existing failures are unrelated to this PR (tracked in #834 ).
This PR only modifies Dockerfile and .dockerignore — no Python code changed.

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

The 16 test failures visible in the test output are pre-existing issues unrelated to this PR and are being addressed separately in PR #834. This PR touches only Dockerfile and .dockerignore and has zero impact on application behavior.

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[Aryanbansal-05]

The CI test failures are pre-existing issues caused by a broken import in test_basic.py (WEIGHT_LEVEL not found in utils.recommender). These are unrelated to this PR and are already fixed in PR #834. This PR only modifies Dockerfile and .dockerignore with no impact on application code or tests.

[Aryanbansal-05]

Hi @komalharshita,
Just a friendly nudge — this PR has been open for a few days and just needs a review and merge whenever you have a moment. The failing CI checks are due to the pre-existing test import issue covered in PR #834, not related to these Docker changes. Thanks!