refactor: centralize agent tool registry

tests/test_core.py

@@ -11,6 +11,7 @@ from assistant_bot.agent import (
     execute_agent_tool,
     parse_agent_decision,
 )
+from assistant_bot.agent_tools import AGENT_TOOLS
 from assistant_bot.reminders import parse_reminder, unit_to_timedelta
 from assistant_bot.storage import AssistantStorage
 
@@ -78,6 +79,10 @@ class AgentToolContractTests(unittest.TestCase):
     def test_prompt_exposes_all_supported_tool_names(self) -> None:
         prompt = build_agent_tool_prompt(ZoneInfo("UTC"))
 
+        self.assertEqual(
+            tuple(tool.name for tool in AGENT_TOOLS),
+            self.TOOL_NAMES,
+        )
         for tool_name in self.TOOL_NAMES:
             with self.subTest(tool_name=tool_name):
                 self.assertIn(tool_name, prompt)