fix: resolve all call-non-callable ty diagnostics across codebase

Replace hasattr() duck-typing with isinstance() checks for DiscordAdapter
in gateway/run.py, add TypedDict for IMAGEGEN_BACKENDS in tools_config.py,
properly type fal_client getattr'd callables in image_generation_tool.py,
fix dict[str, object] → Callable annotation in approval.py, use
isinstance(BaseModel) in web_tools.py, capture _message_handler to local
in base.py, rename shadowed list_distributions parameter in batch_runner.py,
and remove dead queue_message branch.

scripts/batch_runner.py

@@ -1130,7 +1130,7 @@ def main(
     num_workers: int = 4,
     resume: bool = False,
     verbose: bool = False,
-    list_distributions: bool = False,
+    show_distributions: bool = False,
     ephemeral_system_prompt: str = None,
     log_prefix_chars: int = 100,
     providers_allowed: str = None,
@@ -1158,7 +1158,7 @@ def main(
         num_workers (int): Number of parallel worker processes (default: 4)
         resume (bool): Resume from checkpoint if run was interrupted (default: False)
         verbose (bool): Enable verbose logging (default: False)
-        list_distributions (bool): List available toolset distributions and exit
+        show_distributions (bool): List available toolset distributions and exit
         ephemeral_system_prompt (str): System prompt used during agent execution but NOT saved to trajectories (optional)
         log_prefix_chars (int): Number of characters to show in log previews for tool calls/responses (default: 20)
         providers_allowed (str): Comma-separated list of OpenRouter providers to allow (e.g. "anthropic,openai")
@@ -1190,10 +1190,10 @@ def main(
                                --prefill_messages_file=configs/prefill_opus.json
         
         # List available distributions
-        python batch_runner.py --list_distributions
+        python batch_runner.py --show_distributions
     """
     # Handle list distributions
-    if list_distributions:
+    if show_distributions:
         from toolset_distributions import print_distribution_info
 
         print("📊 Available Toolset Distributions")