Initial commit: Flask battery tracker app

- Flask + SQLAlchemy (MariaDB-compatible schema) battery tracking web app
- 40 pre-seeded batteries (Eneloop, BONAI, Energizer NiMH) across 5 devices
- Business rules: block retired assignment, brand-mix warnings, capacity checks
- Mobile-friendly Jinja2 templates with inline CSS
- waitress WSGI server via systemd user service (sbin/install-service.sh)
- SQLite → MariaDB migration script (migrate_to_mariadb.py)
- 26 passing acceptance tests (pytest + Flask test client)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

models.py

@@ -0,0 +1,52 @@
+from sqlalchemy import Column, Integer, String, Text, ForeignKey
+from sqlalchemy.orm import declarative_base, relationship
+
+Base = declarative_base()
+
+
+class Device(Base):
+    __tablename__ = "device"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(100), nullable=False, unique=True)
+    battery_slots = Column(Integer, nullable=False, default=1)
+    notes = Column(Text, nullable=True)
+
+    batteries = relationship("Battery", back_populates="device")
+
+    def installed_count(self):
+        return sum(1 for b in self.batteries if b.status == "installed")
+
+    def installed_brands(self):
+        return set(b.brand for b in self.batteries if b.status == "installed")
+
+    def has_mixed_brands(self):
+        return len(self.installed_brands()) > 1
+
+    def __repr__(self):
+        return f"<Device {self.name}>"
+
+
+class Battery(Base):
+    __tablename__ = "battery"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    label = Column(String(50), nullable=False, unique=True)
+    brand = Column(String(100), nullable=False)
+    status = Column(String(20), nullable=False, default="available")
+    device_id = Column(Integer, ForeignKey("device.id", ondelete="SET NULL"), nullable=True)
+    notes = Column(Text, nullable=True)
+
+    device = relationship("Device", back_populates="batteries")
+
+    def is_available(self):
+        return self.status == "available"
+
+    def is_retired(self):
+        return self.status == "retired"
+
+    def is_installed(self):
+        return self.status == "installed"
+
+    def __repr__(self):
+        return f"<Battery {self.label}>"