refactor(agent): gate sustained goals behind explicit /goal

Replace the legacy long-goal skill contract with command-scoped goal tools and runtime guidance. Keep goal state durable across continuations while restricting create and replace mutations to explicit user /goal turns.

tests/tools/test_filesystem_tools.py

@@ -79,10 +79,10 @@ class TestReadFileTool:
 
     @pytest.mark.asyncio
     async def test_workspace_relative_builtin_skill_read_falls_back_to_packaged_skill(self, tool):
-        result = await tool.execute(path="skills/long-goal/SKILL.md", limit=5)
+        result = await tool.execute(path="skills/cron/SKILL.md", limit=5)
 
         assert "Error" not in result
-        assert "long-goal" in result.lower()
+        assert "cron" in result.lower()
 
     @pytest.mark.asyncio
     async def test_missing_path_returns_clear_error(self, tool):