fix(BA-5832): annotate _load_items return type for mypy

`list[dict]` was missing the value type parameter and `json.loads`
returns `Any`, so mypy flagged 9 type-arg / no-any-return errors. Use
`list[dict[str, Any]]` and `cast()` to keep CLAUDE.md's
no-`# type: ignore` rule.

Also picks up a stale BA-5829 ruff format on Fragment node.py from the
JSON-scalar fix cascade.

Author: jopemachine

src/ai/backend/client/cli/v2/admin/app_config_fragment.py

@@ -5,6 +5,7 @@
 import asyncio
 import json
 from pathlib import Path
+from typing import Any, cast
 
 import click
 
@@ -21,11 +22,11 @@ def app_config_fragment() -> None:
     """Admin AppConfigFragment commands (cross-scope search + bulk-only writes)."""
 
 
-def _load_items(items_arg: str) -> list[dict]:
+def _load_items(items_arg: str) -> list[dict[str, Any]]:
     """Accept JSON string or `@file.json` path."""
     if items_arg.startswith("@"):
-        return json.loads(Path(items_arg[1:]).read_text())
-    return json.loads(items_arg)
+        return cast("list[dict[str, Any]]", json.loads(Path(items_arg[1:]).read_text()))
+    return cast("list[dict[str, Any]]", json.loads(items_arg))
 
 
 @app_config_fragment.command()

src/ai/backend/client/cli/v2/admin/app_config_policy.py

@@ -5,6 +5,7 @@
 import asyncio
 import json
 from pathlib import Path
+from typing import Any, cast
 
 import click
 
@@ -16,11 +17,11 @@ def app_config_policy() -> None:
     """Admin AppConfigPolicy commands (bulk-only)."""
 
 
-def _load_items(items_arg: str) -> list[dict]:
+def _load_items(items_arg: str) -> list[dict[str, Any]]:
     """Accept JSON string or `@file.json` path."""
     if items_arg.startswith("@"):
-        return json.loads(Path(items_arg[1:]).read_text())
-    return json.loads(items_arg)
+        return cast("list[dict[str, Any]]", json.loads(Path(items_arg[1:]).read_text()))
+    return cast("list[dict[str, Any]]", json.loads(items_arg))
 
 
 @app_config_policy.command(name="bulk-create")

src/ai/backend/client/cli/v2/my/app_config.py

@@ -5,6 +5,7 @@
 import asyncio
 import json
 from pathlib import Path
+from typing import Any, cast
 
 import click
 
@@ -71,11 +72,11 @@ async def _run() -> None:
     asyncio.run(_run())
 
 
-def _load_items(items_arg: str) -> list[dict]:
+def _load_items(items_arg: str) -> list[dict[str, Any]]:
     """Accept JSON string or `@file.json` path."""
     if items_arg.startswith("@"):
-        return json.loads(Path(items_arg[1:]).read_text())
-    return json.loads(items_arg)
+        return cast("list[dict[str, Any]]", json.loads(Path(items_arg[1:]).read_text()))
+    return cast("list[dict[str, Any]]", json.loads(items_arg))
 
 
 @app_config.command(name="bulk-create")