create tabular orchestration file.

move tabular processing in the chat to its own python file

[application/single_app/route_backend_chats.py]
f"{missing_sheet_feedback}"
f"FILE SCHEMAS:\n"
f"{schema_context}\n\n"
"AVAILABLE FUNCTIONS: lookup_value, aggregate_column, filter_rows, query_tabular_data, "

Move this to a markdown and parse it in and move the functions to another file or the plugin, and call that method.

Start by reading application/single_app/route_backend_chats.py, especially the embedded tabular-processing prompt and the listed functions. Separate the tabular orchestration and move the prompt content and functions as described, then verify that chat tabular processing still works through the new file or plugin.

Written by the indexing model from the issue text.