fix event_queries crash without pg_stat_statements, fix IdleTx color in top_by_type

P0: event_queries()/event_queries_at() referenced pg_stat_statements
at plan time even when v_has_pgss=false. Split into two RETURN QUERY
branches like top_queries() does.

P2: top_by_type passes 'IdleTx:*' to _wait_color which used exact
match (p_event = 'IdleTx'). Changed to LIKE 'IdleTx%' so 'IdleTx:*'
matches correctly.

P3: Updated stale color scheme comment (was 4-bit ANSI names).

Found by Max's v1.2 review on PG18 without pg_stat_statements.

Author: NikolayS