refactor: align backend layout and supabase infra

Consolidate backend modules/tests under the backend package while syncing Supabase compose/env config and related plans.

backend/src/v1/profile/schemas.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+from pydantic import AnyHttpUrl, BaseModel, Field, field_validator, model_validator
+
+
+class ProfileResponse(BaseModel):
+    id: str
+    username: str
+    display_name: str | None = None
+    avatar_url: str | None = None
+    bio: str | None = None
+
+
+class ProfileUpdateRequest(BaseModel):
+    display_name: str | None = Field(default=None, max_length=50)
+    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) -> "ProfileUpdateRequest":
+        if self.display_name is None and self.avatar_url is None and self.bio is None:
+            raise ValueError("At least one field must be provided")
+        return self