Fix/issue 2341 alembic migrations

[Prateek2007-cmd]

Description

Resolves Issue #2341 (Direct Schema Creation over Migrations).

The backend previously relied on SQLAlchemy's metadata.create_all() at startup. This "development-only" approach is a severe architectural liability in production, as it cannot gracefully handle schema evolutions (like adding or dropping columns) without dropping the entire database, risking catastrophic data loss.

This PR introduces Alembic to manage database schemas via deterministic, version-controlled migration scripts.

Changes Made

• Removed Dangerous Auto-Creation: Purged create_all() from backend/app/main.py.
• Alembic Pipeline: Initialized the alembic environment, pointing alembic.ini to the SQLite cara.db.
• Target Metadata: Configured alembic/env.py to securely read from backend.app.models.Base.metadata to support --autogenerate.
• Initial Revision: Generated the first automated migration script encompassing all existing models.

Type of Change

• Architectural Improvement
• Technical Debt Remediation

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