Add Seismo Fleet Manager backend v0.1

Implemented FastAPI backend with SQLite database for tracking seismograph fleet status:
- database.py: SQLAlchemy setup with SQLite
- models.py: Emitter model with id, unit_type, last_seen, last_file, status, notes
- routes.py: POST /emitters/report and GET /fleet/status endpoints
- main.py: FastAPI app initialization with CORS support
- requirements.txt: Dependencies (FastAPI, SQLAlchemy, uvicorn)

database.py

@@ -0,0 +1,22 @@
+from sqlalchemy import create_engine
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker
+
+SQLALCHEMY_DATABASE_URL = "sqlite:///./seismo_fleet.db"
+
+engine = create_engine(
+    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+Base = declarative_base()
+
+
+def get_db():
+    """Dependency for database sessions"""
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()