MAESTRO: add captcha verification flow

backend/app/schemas/captcha.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class CaptchaChallenge(BaseModel):
+    model_config = ConfigDict(populate_by_name=True)
+
+    challenge_token: str = Field(alias="challengeToken")
+    image_base64: str = Field(alias="imageBase64")
+
+
+class CaptchaVerifyRequest(BaseModel):
+    model_config = ConfigDict(populate_by_name=True)
+
+    challenge_token: str = Field(alias="challengeToken")
+    answer: str
+
+
+class CaptchaVerifyResponse(BaseModel):
+    model_config = ConfigDict(populate_by_name=True)
+
+    success: bool
+    bypass_token: str | None = Field(default=None, alias="bypassToken")
+
+
+__all__ = [
+    "CaptchaChallenge",
+    "CaptchaVerifyRequest",
+    "CaptchaVerifyResponse",
+]