feat(setup): T03 create requirements.txt with dependencies

- Add requirements.txt with all core dependencies:
  - FastAPI 0.104.1, uvicorn 0.24.0
  - SQLAlchemy 2.0.23, Alembic 1.12.1
  - Pydantic 2.5.0, pydantic-settings 2.1.0
  - python-jose 3.3.0, passlib 1.7.4, cryptography 41.0.7
  - httpx 0.25.2, pytest 7.4.3, pytest-asyncio 0.21.1, pytest-cov 4.1.0
- Add test_requirements.py with 15 unit tests
- All tests passing (15/15)

Refs: T03

requirements.txt

@@ -0,0 +1,30 @@
+# ===========================================
+# OpenRouter API Key Monitor - Dependencies
+# ===========================================
+
+# Web Framework
+fastapi==0.104.1
+uvicorn[standard]==0.24.0
+python-multipart==0.0.6
+
+# Database
+sqlalchemy==2.0.23
+alembic==1.12.1
+
+# Validation & Settings
+pydantic==2.5.0
+pydantic-settings==2.1.0
+
+# Authentication & Security
+python-jose[cryptography]==3.3.0
+passlib[bcrypt]==1.7.4
+cryptography==41.0.7
+
+# HTTP Client
+httpx==0.25.2
+
+# Testing
+pytest==7.4.3
+pytest-asyncio==0.21.1
+pytest-cov==4.1.0
+httpx==0.25.2