feat(portfolio): add stock consolidation domain and schema

app/schemas/corporate_actions.py

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+from datetime import date, datetime
+from decimal import Decimal
+from typing import Literal
+from pydantic import BaseModel, ConfigDict, Field, model_validator
+
+# Corporate actions (stock_consolidation-only, issue #34)
+class CorporateActionRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    action_type: Literal["stock_consolidation"] = "stock_consolidation"
+    effective_date: date
+    quantity_before: Decimal = Field(..., gt=0, max_digits=20, decimal_places=8)
+    quantity_after: Decimal = Field(..., gt=0, max_digits=20, decimal_places=8)
+    evidence_ref: str = Field(..., min_length=1, max_length=500)
+    confirm_daemon_managed: bool = False
+
+    @model_validator(mode="after")
+    def valid_ratio(self):
+        if self.quantity_after >= self.quantity_before:
+            raise ValueError("quantity_after must be less than quantity_before")
+        return self
+
+class CorporateActionResponse(BaseModel):
+    corporate_action_id: str
+    ledger_entry_id: int
+    portfolio_id: str
+    action_type: Literal["stock_consolidation"]
+    effective_date: date
+    quantity_before: Decimal
+    quantity_after: Decimal
+    average_price_before: Decimal
+    average_price_after: Decimal
+    total_cost_basis: Decimal
+    cash_balance: Decimal
+    profit_buffer: Decimal
+    evidence_ref: str
+    actor_user_id: str | None = None
+    recorded_at: datetime
+    idempotent_replay: bool = False