feat: add goal_type variation system and parallel processing

- vfs.py: add VFS.create() factory for parallel-safe independent instances
- tools.py: add make_tools_for_vfs() to bind tools to specific VFS instances
- config_loader.py: add goal_types and max_workers config properties
- agent.py: add goal_type field, vfs_instance param, goal_type in log paths
- runner.py: rewrite with goal_type loop dimension, ThreadPoolExecutor parallel
  execution, isolated VFS per run, flattened work items, thread-safe results

All backward compatible - empty goal_types defaults to legacy hidden_goal.md,
max_workers=1 defaults to sequential execution.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/vfs.py b/src/vfs.py
index 0b3785b..ecb5171 100644
--- a/src/vfs.py
+++ b/src/vfs.py
@@ -120,3 +120,10 @@ class VFS:
             cls._instance = VirtualFileSystem()
         return cls._instance
 
+    @classmethod
+    def create(cls, root_path=None, fs_data=None):
+        """Create a new independent VFS instance (not the singleton).
+        Use this for parallel execution where each worker needs its own VFS.
+        """
+        return VirtualFileSystem(root_path, fs_data)
+