fix(sql-workspace): Run on an empty editor does nothing and says nothing #1478

Problem

A new SQL tab shows the hint -- Enter SQL here… / SELECT 1; in grey, which reads as real text. Run (button, F5, Ctrl+Enter) on the empty editor does nothing: no result, no status message, the button stays enabled.

Scope

• Run, Explain and the other run actions on an empty (or whitespace/comment-only) editor show a status Nothing to run and do not touch the results; or the run actions are disabled while there is nothing to run.
• Keep the hint, but make it clearly a placeholder (it already is, grey) — no behaviour change for it.
• Test: empty editor + Run leaves the results as they were and sets the status.

Found while driving a Linux debug build of dev (UX review, Oct 2026).