Changes prakhar

[Prakhar-Sethi012]

What this PR does:

Initializes the core database infrastructure, implements a modular FastAPI architecture, and establishes isolated Alembic migrations for future-proofing our vector database.

Key Changes:

• Docker Infrastructure: Containerized pgvector inside docker-compose.yml. Configured host port to 5433 to bypass potential local Windows PostgreSQL conflicts.
• Modular Architecture: Split database logic into Enterprise FastAPI standards (app/models for SQLAlchemy, app/schemas for Pydantic).
• Alembic CI/CD: Generated 3 distinct, isolated migration scripts for safety and modularity:
  1. files (Metadata and GIN tags index)
  2. file_content (pgvector 384-dimensions and Full Text Search tsvector)
  3. file_relationships (Semantic similarity mapping)
• Data Contracts: Established baseline Pydantic schemas (DocumentIngest, DocumentSearchResponse) ready for Backend 2 to expand upon.

Testing:

• Confirmed successful local build via docker-compose up -d.
• Successfully executed alembic upgrade head to populate the pg17 vector database.