ux(sql-workspace): readable query errors: driver message first, details folded and unwrapped, Copy (#1557)

[ZhuchkaTriplesix]

Refs #1557 (items 1 and 2; the caret jump and the MongoDB panel are not in this PR).

A failed query showed the driver exception as-is: the same message twice (SqliteFfiException(...) around DatabaseException(...)), class names, and the statement the app wraps around the user's SQL (SELECT * FROM ( ... ) LIMIT 5000, #1144), with a position that counts from that wrapper.

QueryErrorText.parse(raw) (lib/core/database/query_error_text.dart, pure):

• summary: the driver's message alone. SQLite SqliteException(n): while ..., <message>, ... (code n), PostgreSQL Severity.error XXXXX: <message> (without detail: / hint:), MySQL MySQLServerException [n]: <message>; anything else its first line (a leading Exception: dropped). Cut at 300 characters.
• detail: the whole text with the app's SELECT * FROM (\n...\n) wrapper and the row limit after it replaced by the user's SQL, and the misleading (at position N) removed when a wrapper was there. Text without a wrapper is unchanged.

Results pane (ResultsTab): the summary is the headline (selectable, normal text colour); when there is more, Show details unfolds the detail (scrolls in a short pane, as before) and Copy error copies it ("Copied" for 2 s). A one-line error looks as before. Timeouts and other app messages go through the same path and read as before.

Example from the issue now reads no such column: u.name.

Not done: putting the caret / a squiggle at the error position (needs the position translated back to the user's text), and the same panel for MongoDB's Query Error.

Tests: the parser for SQLite (the issue's example), PostgreSQL, MySQL, a plain message, text without a wrapper and a very long message; the pane shows the headline with details folded, unfolds them without the wrapper, copies the unwrapped text, and shows no details for a one-line error. The existing error-pane tests are unchanged.