fix(sqlite): do not share the SQL-editor Database with Table Browser #794

Summary

Pool key is id::readWrite. QueryaSwitchingBody keeps home (SQL) mounted under the table. Both acquire readWrite → one Database. Table Save runs BEGIN TRANSACTION on a connection that may already be in a transaction from the SQL tab: cannot start a transaction within a transaction. ATTACH / PRAGMA from SQL leak into the grid.

Unlike Postgres, SQLite home has no open-transaction warning on tab switch.

Scope

• Separate pool keys (or drop the SQL lease while a table is focused).
• Do not BEGIN if the session is already in a transaction (or always use a dedicated Save connection).
• Warn or refuse opening a table while the SQL tab has an open BEGIN.
• ATTACH from SQL must not change what Table Browser FROM resolves to.

Out of scope

• Read-only honor on the grid (separate issue).
• Postgres shared-socket (fix(postgres): do not share the SQL-editor read-write socket with Table Browser #785) — same class, SQLite-specific Save error is nested BEGIN.