fix: remove private symbols from __all__ per collab-opus P1 finding

Strip _-prefixed symbols from grounding/__init__.py __all__ to follow
PEP 8 convention. Private helpers remain importable for the facade but
are excluded from wildcard imports.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Brian Krafft

openspace/agents/grounding/__init__.py

@@ -60,7 +60,6 @@
     # execution
     "process",
     # messages
-    "_MAX_SINGLE_CONTENT_CHARS",
     "cap_message_content",
     "truncate_messages",
     # prompts
@@ -75,15 +74,4 @@
     "generate_final_summary",
     "record_agent_execution",
     "remove_previous_guidance",
-    # tools
-    "_get_available_tools",
-    "_load_all_tools",
-    # visual
-    "_visual_analysis_callback",
-    "_enhance_result_with_visual_context",
-    "_select_key_screenshots",
-    # workspace
-    "_check_workspace_artifacts",
-    "_get_workspace_path",
-    "_scan_workspace_files",
 ]