M8-R08: add atomic meter close and binding transfer

app/schemas/meter.py

@@ -146,3 +146,9 @@ class MeterPatchRequest(BaseModel):
             "Triggers billing recompute over the affected window."
         ),
     )
+
+
+class MeterCloseRequest(BaseModel):
+    """Close the active meter epoch at an exclusive end boundary."""
+
+    ended_at: datetime

app/schemas/meter_source.py

@@ -135,6 +135,12 @@ class BindingPatch(BaseModel):
     ended_at: datetime | None = None
 
 
+class BindingTransferRequest(BaseModel):
+    from_binding_uuid: str = Field(..., min_length=1, max_length=36)
+    to_source_channel_uuid: str = Field(..., min_length=1, max_length=36)
+    effective_at: datetime
+
+
 class BindingResponse(BaseModel):
     uuid: str
     meter_id: int
@@ -149,3 +155,8 @@ class BindingResponse(BaseModel):
 class BindingListResponse(BaseModel):
     items: list[BindingResponse]
     total: int
+
+
+class BindingTransferResponse(BaseModel):
+    closed_binding: BindingResponse
+    created_binding: BindingResponse