feat: Phase 6 — alarm system (auto-generate, list, acknowledge)

- Add Alarm model with tenant/part/machine relationships and 3 indexes
- Add alembic migration c5d6e7f8a9b0_add_alarms
- Add alarms API: list (filter by ack/severity), summary, acknowledge
- Auto-generate alarms on counter update (threshold warning, critical at 100%)
- Duplicate alarm prevention for same part+alarm_type
- Add alarms frontend page with active/acknowledged tabs, summary badges
- 9 new tests (67/67 total passing)

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

src/database/models.py

@@ -305,3 +305,33 @@ class InspectionRecord(Base):
         ),
         Index("ix_records_session", "session_id"),
     )
+
+
+class Alarm(Base):
+    __tablename__ = "alarms"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    tenant_id = Column(String(50), ForeignKey("tenants.id"), nullable=False)
+    equipment_part_id = Column(
+        UUID(as_uuid=True), ForeignKey("equipment_parts.id"), nullable=False
+    )
+    machine_id = Column(UUID(as_uuid=True), ForeignKey("machines.id"), nullable=False)
+    alarm_type = Column(String(30), nullable=False)  # threshold | critical
+    severity = Column(String(20), nullable=False)  # warning | critical
+    message = Column(String(500), nullable=False)
+    lifecycle_pct_at_trigger = Column(Float, nullable=False)
+    is_acknowledged = Column(Boolean, default=False)
+    acknowledged_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    acknowledged_at = Column(TIMESTAMP(timezone=True), nullable=True)
+    created_at = Column(TIMESTAMP(timezone=True), default=utcnow)
+
+    tenant = relationship("Tenant")
+    equipment_part = relationship("EquipmentPart")
+    machine = relationship("Machine")
+    acknowledged_user = relationship("User")
+
+    __table_args__ = (
+        Index("ix_alarms_tenant_ack", "tenant_id", "is_acknowledged"),
+        Index("ix_alarms_tenant_severity", "tenant_id", "severity"),
+        Index("ix_alarms_tenant_part", "tenant_id", "equipment_part_id"),
+    )