fix: move SQL queries from database/ to docs/queries

SQL query files (playground, test queries) are development documentation,
not production database files. They belong in docs/ alongside other documentation.

docs/queries/playground.sql

@@ -0,0 +1,18 @@
+SELECT * FROM public.test_transaction_llm
+ORDER BY id ASC ;
+
+
+select * from backend.transactions;
+
+Select * from 
+backend.transactions as t
+left join backend.transaction_outputs as tout on t.id = tout.transaction_id
+left join backend.prompt_templates as prt on tout.prompt_id = prt.prompt_id
+--where t.id = 2
+order by transaction_id, tout.prompt_id;
+
+select * from backend.prompt_templates;
+
+Select * from public.companies;
+
+select * from public.transactions;