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)

models.py

@@ -0,0 +1,18 @@
+from sqlalchemy import Column, String, DateTime
+from datetime import datetime
+from database import Base
+
+
+class Emitter(Base):
+    """Emitter model representing a seismograph unit in the fleet"""
+    __tablename__ = "emitters"
+
+    id = Column(String, primary_key=True, index=True)
+    unit_type = Column(String, nullable=False)
+    last_seen = Column(DateTime, default=datetime.utcnow)
+    last_file = Column(String, nullable=False)
+    status = Column(String, nullable=False)  # OK, Pending, Missing
+    notes = Column(String, nullable=True)
+
+    def __repr__(self):
+        return f"<Emitter(id={self.id}, type={self.unit_type}, status={self.status})>"