refactor: Phase 1 - rename and simplify backend schemas

backend/src/v1/users/schemas.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from pydantic import (
+    AnyHttpUrl,
+    BaseModel,
+    ConfigDict,
+    Field,
+    field_validator,
+    model_validator,
+)
+
+
+class UserResponse(BaseModel):
+    id: str
+    username: str
+    avatar_url: str | None = None
+    bio: str | None = None
+
+
+class UserUpdateRequest(BaseModel):
+    model_config: ClassVar[ConfigDict] = ConfigDict(extra="forbid")
+
+    username: str | None = Field(default=None, min_length=3, max_length=30)
+    avatar_url: str | None = Field(default=None)
+    bio: str | None = Field(default=None, max_length=200)
+
+    @field_validator("avatar_url", mode="before")
+    @classmethod
+    def validate_avatar_url(cls, v: str | None) -> str | None:
+        if v is None:
+            return None
+        parsed = AnyHttpUrl(v)
+        if parsed.scheme not in ("http", "https"):
+            raise ValueError("avatar_url must use http or https scheme")
+        return str(parsed)
+
+    @model_validator(mode="after")
+    def require_one_field(self) -> "UserUpdateRequest":
+        if self.username is None and self.avatar_url is None and self.bio is None:
+            raise ValueError("At least one field must be provided")
+        return self