feat(api): add REST API blueprint for snippets

[AdvaitVarhade]

What changed

• Created new Flask blueprint app/api.py mounted at /api.
• Implemented GET /api/snippets with query filtering (?q=, ?language=, ?tag=) returning JSON.
• Implemented GET /api/snippets/ returning single snippet JSON or 404 for invalid/missing IDs.
• Updated format_snippet in app/models.py to handle ISO datetime serialization.
• Added endpoint documentation to README.md.
• Added comprehensive unit tests in tests/test_api.py.

Please check and tell if any changes are required

[AdvaitVarhade]

Hi @byteofhoney, following up on PR #28 where I created the REST API blueprint (GET /api/snippets with query filtering, GET /api/snippets/<id>), updated JSON serialization, added README documentation, and unit test coverage. Let me know if you have any feedback or if you'd like anything adjusted, Thank you.