refactor: simplify mqtt pipeline state and remove event table

backend/app/models.py

@@ -126,9 +126,7 @@ class TerminalMessageRaw(SQLModel, table=True):
     payload_sha256: str = Field(default="", max_length=64, index=True)
     qos: int = 0
     retain: bool = False
-    parse_status: str = Field(default="pending", max_length=32, index=True)
-    parse_attempts: int = 0
-    next_retry_at: datetime | None = Field(
+    parsed_at: datetime | None = Field(
         default=None,
         sa_type=DateTime(timezone=True),  # type: ignore
         index=True,
@@ -140,27 +138,6 @@ class TerminalMessageRaw(SQLModel, table=True):
     )
 
 
-class TerminalObservationEvent(SQLModel, table=True):
-    __tablename__ = "terminal_observation_event"
-
-    id: uuid.UUID = Field(default_factory=uuid.uuid4, primary_key=True)
-    raw_id: uuid.UUID = Field(
-        foreign_key="terminal_message_raw.id", nullable=False, index=True
-    )
-    device_id: str = Field(max_length=255, index=True)
-    event_time: datetime = Field(
-        default_factory=get_datetime_utc,
-        sa_type=DateTime(timezone=True),  # type: ignore
-        index=True,
-    )
-    event_type: str = Field(max_length=64, index=True)
-    payload_json: dict[str, Any] = Field(default_factory=dict, sa_type=JSON)
-    created_at: datetime = Field(
-        default_factory=get_datetime_utc,
-        sa_type=DateTime(timezone=True),  # type: ignore
-    )
-
-
 class TerminalDeviceState(SQLModel, table=True):
     __tablename__ = "terminal_device_state"