modelgen: recurse through nested generics in list resolvers

_get_list_inner (Pydantic) and _resolve_ts_list (TypeScript) collapsed
nested generics to "str" / "string[]" — so List[List[int]] became
List[str] and List[Dict[str,Any]] became List[str]. Fix recurses on
list-of-list and falls back to Dict[str,Any] / Record<string,unknown>
for list-of-dict.

Regenerated outputs:
- core/gpu/models/models.py: SegmentFieldResponse.boundary now
  List[List[int]], unblocking /segment_field which was 500ing on every
  request with pydantic ValidationError
- core/db/models.py + ui/common/types/generated.ts: Brand.airings now
  matches its source schema (List[Dict[str,Any]] / Record<string,unknown>[])

modelgen/types.py

@@ -8,6 +8,8 @@ Used by generators to convert Python types to target framework types.
 import dataclasses as dc
 from typing import Any, Callable, get_args
 
+from .helpers import get_origin_name
+
 # =============================================================================
 # Django Type Mappings
 # =============================================================================
@@ -38,7 +40,7 @@ DJANGO_SPECIAL: dict[str, str] = {
 
 
 def _get_list_inner(type_hint: Any) -> str:
-    """Get inner type of List[T] for Pydantic."""
+    """Get inner type of List[T] for Pydantic. Recurses for nested generics."""
     args = get_args(type_hint)
     if args:
         inner = args[0]
@@ -46,6 +48,11 @@ def _get_list_inner(type_hint: Any) -> str:
             return {str: "str", int: "int", float: "float", bool: "bool"}[inner]
         if isinstance(inner, type) and dc.is_dataclass(inner):
             return inner.__name__
+        origin = get_origin_name(inner)
+        if origin == "list":
+            return f"List[{_get_list_inner(inner)}]"
+        if origin == "dict":
+            return "Dict[str, Any]"
     return "str"
 
 
@@ -69,7 +76,7 @@ PYDANTIC_RESOLVERS: dict[Any, Callable[[Any], str]] = {
 
 
 def _resolve_ts_list(base: Any) -> str:
-    """Resolve TypeScript list type."""
+    """Resolve TypeScript list type. Recurses for nested generics."""
     args = get_args(base)
     if args:
         inner = args[0]
@@ -81,6 +88,11 @@ def _resolve_ts_list(base: Any) -> str:
             return "boolean[]"
         elif isinstance(inner, type) and dc.is_dataclass(inner):
             return f"{inner.__name__}[]"
+        origin = get_origin_name(inner)
+        if origin == "list":
+            return f"{_resolve_ts_list(inner)}[]"
+        if origin == "dict":
+            return "Record<string, unknown>[]"
     return "string[]"