docs: add migration + fix icon

docs/migration/v2.md

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+# Migrating to v2.0
+
+This page covers every breaking change introduced in **v2.0** and the steps required to update your code.
+
+---
+
+## CRUD
+
+### `schema` is now required in `offset_paginate()` and `cursor_paginate()`
+
+Calls that omit `schema` will now raise a `TypeError` at runtime.
+
+Previously `schema` was optional; omitting it returned raw SQLAlchemy model instances inside the response. It is now a required keyword argument and the response always contains serialized schema instances.
+
+=== "Before (`v1`)"
+
+    ```python
+    # schema omitted — returned raw model instances
+    result = await UserCrud.offset_paginate(session, page=1)
+    result = await UserCrud.cursor_paginate(session, cursor=token)
+    ```
+
+=== "Now (`v2`)"
+
+    ```python
+    result = await UserCrud.offset_paginate(session, page=1, schema=UserRead)
+    result = await UserCrud.cursor_paginate(session, cursor=token, schema=UserRead)
+    ```
+
+### `as_response` removed from `create()`, `get()`, and `update()`
+
+Passing `as_response` to these methods will raise a `TypeError` at runtime.
+
+The `as_response=True` shorthand is replaced by passing a `schema` directly. The return value is a `Response[schema]` when `schema` is provided, or the raw model instance when it is not.
+
+=== "Before (`v1`)"
+
+    ```python
+    user = await UserCrud.create(session, data, as_response=True)
+    user = await UserCrud.get(session, filters, as_response=True)
+    user = await UserCrud.update(session, data, filters, as_response=True)
+    ```
+
+=== "Now (`v2`)"
+
+    ```python
+    user = await UserCrud.create(session, data, schema=UserRead)
+    user = await UserCrud.get(session, filters, schema=UserRead)
+    user = await UserCrud.update(session, data, filters, schema=UserRead)
+    ```
+
+### `delete()`: `as_response` renamed and return type changed
+
+`as_response` is gone, and the plain (non-response) call no longer returns `True`.
+
+Two changes were made to `delete()`:
+
+1. The `as_response` parameter is renamed to `return_response`.
+2. When called without `return_response=True`, the method now returns `None` on success instead of `True`.
+
+=== "Before (`v1`)"
+
+    ```python
+    ok = await UserCrud.delete(session, filters)
+    if ok:  # True on success
+        ...
+
+    response = await UserCrud.delete(session, filters, as_response=True)
+    ```
+
+=== "Now (`v2`)"
+
+    ```python
+    await UserCrud.delete(session, filters)  # returns None
+
+    response = await UserCrud.delete(session, filters, return_response=True)
+    ```
+
+### `paginate()` alias removed
+
+Any call to `crud.paginate(...)` will raise `AttributeError` at runtime.
+
+The `paginate` shorthand was an alias for `offset_paginate`. It has been removed; call `offset_paginate` directly.
+
+=== "Before (`v1`)"
+
+    ```python
+    result = await UserCrud.paginate(session, page=2, items_per_page=20, schema=UserRead)
+    ```
+
+=== "Now (`v2`)"
+
+    ```python
+    result = await UserCrud.offset_paginate(session, page=2, items_per_page=20, schema=UserRead)
+    ```
+
+---
+
+## Exceptions
+
+### Missing `api_error` raises `TypeError` at class definition time
+
+Unfinished or stub exception subclasses that previously compiled fine will now fail on import.
+
+In `v1`, a subclass without `api_error` would only fail when the exception was raised. In `v2`, `__init_subclass__` validates this at class definition time.
+
+=== "Before (`v1`)"
+
+    ```python
+    class MyError(ApiException):
+        pass  # fine until raised
+    ```
+
+=== "Now (`v2`)"
+
+    ```python
+    class MyError(ApiException):
+        pass  # TypeError: MyError must define an 'api_error' class attribute.
+    ```
+
+For shared base classes that are not meant to be raised directly, use `abstract=True`:
+
+```python
+class BillingError(ApiException, abstract=True):
+    """Base for all billing-related errors — not raised directly."""
+
+class PaymentRequiredError(BillingError):
+    api_error = ApiError(code=402, msg="Payment Required", desc="...", err_code="BILLING-402")
+```
+
+---
+
+## Schemas
+
+### `Pagination` alias removed
+
+`Pagination` was already deprecated in `v1` and is fully removed in `v2`, you now need to use [`OffsetPagination`](../reference/schemas.md#fastapi_toolsets.schemas.OffsetPagination) or [`CursorPagination`](../reference/schemas.md#fastapi_toolsets.schemas.CursorPagination).