feat: lock concurrent moderation decisions

apps/api/app/schemas.py

@@ -199,11 +199,13 @@ class AdminCatchReportOut(BaseModel):
     moderation_status: str
     comment: str | None
     screenshot_url: str | None
+    moderation_version: int
 
 
 class ModerationUpdate(BaseModel):
     status: str
     reason: str | None = Field(default=None, max_length=1000)
+    expected_version: int = Field(ge=0)
 
     @field_validator("status")
     @classmethod
@@ -236,12 +238,14 @@ class ExternalObservationOut(BaseModel):
     review_note: str | None
     missing_fields: list[str]
     source_payload: dict[str, str | int | float | bool | None]
+    moderation_version: int
 
 
 class ExternalObservationMapping(BaseModel):
     fish_slug: str
     waterbody_slug: str
     note: str | None = Field(default=None, max_length=1000)
+    expected_version: int = Field(ge=0)
 
 
 class ExternalAliasSuggestionOut(BaseModel):
@@ -261,6 +265,11 @@ class AdminModerationHistoryOut(BaseModel):
 
 class ExternalObservationDecision(BaseModel):
     reason: str = Field(min_length=1, max_length=1000)
+    expected_version: int = Field(ge=0)
+
+
+class ExternalObservationAction(BaseModel):
+    expected_version: int = Field(ge=0)
 
 
 class ExternalObservationPublished(BaseModel):