fix(backend): repair unresolvable TYPE_CHECKING imports

Expression classes moved under backend.expression/ and several were renamed
during the derived-DDL refactor, leaving relative-import depths and forward
references in TYPE_CHECKING blocks pointing at modules and classes that no
longer exist. Type checkers and any runtime evaluation of those blocks fail
to resolve them.

Verified statically: every TYPE_CHECKING import in the touched files now
resolves to an existing module and an existing top-level symbol, and no
string annotation references a name absent from the workspace.

Author: vistart

src/rhosocial/activerecord/backend/impl/sqlserver/functions/aggregate.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/bitwise.py

@@ -12,7 +12,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/datetime.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/json.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/math.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/spatial.py

@@ -16,7 +16,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/string.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(

src/rhosocial/activerecord/backend/impl/sqlserver/functions/utility.py

@@ -11,7 +11,7 @@
 
 if TYPE_CHECKING:
     from rhosocial.activerecord.backend.dialect import SQLDialectBase
-    from .dialect import SQLServerDialect
+    from ..dialect import SQLServerDialect
 
 
 def _convert_to_expression(